VEGF-related protein

ABSTRACT

A human VEGF-related protein (VRP) has been identified and isolated that binds to, and stimulates the phosphorylation of, the receptor tyrosine kinase Flt4. The VRP is postulated to be a third member of the VEGF protein family. Also provided are antibodies that bind to VRP and neutralize a biological activity of VRP, compositions containing the VRP or antibody, methods of use, chimeric polypeptides, and a signal polypeptide for VRP.

PRIORITY OF INVENTION

This application is a divisional of pending U.S. patent application Ser.No. 10/346,802, filed on Jan. 17, 2003, now abandoned, which is adivisional of 09/313,299, filed on May 17, 1999, now U.S. Pat. No.6,576,608, which is a divisional application of U.S. patent applicationSer. No. 08/706,054, filed on Aug. 30, 1996, now U.S. Pat. No.6,451,764, which claims the benefit of U.S. Provisional Application Ser.No. 60/003,491, filed on Sep. 8, 1995. All of these applications arehereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains generally to a receptor protein tyrosinekinase (rPTK) ligand. More particularly, the invention relates to anovel ligand, designated VEGF-related protein (VRP) or VH1, which bindsto, and stimulates the phosphorylation of, the Flt4 tyrosine kinasereceptor (also known as the Sal-S1 receptor) and the isolation andrecombinant production of the same.

2. Description of Related Art

The formation of new blood vessels either from differentiatingendothelial cells during embryonic development (vasculogenesis) or frompre-existing vessels during adult life (angiogenesis) is an essentialfeature of organ development, reproduction, and wound healing in higherorganisms. Folkman and Shing, J. Biol. Chem., 267: 10931-10934 (1992);Reynolds et al., FASEB J., 6: 886-892 (1992); Risau et al., Development,102: 471-478 (1988). Angiogenesis is also necessary for certainpathological processes including tumorigenesis (Folkman, NatureMedicine, 1: 27-31 [1995]) and retinopathy. Miller et al., Am. J.Pathol., 145: 574-584 (1994). While several growth factors can stimulateangiogenesis (Klagsbrun and D'Amore, Ann. Rev. Physiol., 53: 217-239[1991]; Folkman and Klagsbrun, Science, 235: 442-447 [1987]), vascularendothelial growth factor (VEGF) (Ferrara et al., Endo. Rev., 13: 18-32[1992]) is a potent angiogenic factor that acts via the endothelialcell-specific receptor tyrosine kinases fms-like tyrosine kinase (Flt1)(Shibuya et al., Oncogene, 5: 519-524 [1990]; deVries et al., Science,255: 989-991 [1992]) and fetal liver kinase (Flk1) (also designatedKDR). Quinn et al., Proc. Natl. Acad. Sci. USA, 90: 7533-7537 (1993);Millauer et al., Cell, 72: 835-846 (1993); Matthews et al., Proc. Natl.Acad. Sci. USA, 88: 9026-9030 (1991); Terman et al., Biochem. Biophys.Res. Commun., 187: 1579-1586 (1992); Terman et al., Oncogene, 6:1677-1683 (1991); Oelrichs et al., Oncogene, 8: 11-18 (1993). These twoVEGF receptors and a third orphan receptor, Flt4 (Pajusola et al.,Cancer Res., 52: 5738-5743 [1992]; Galland et al., Oncogene, 8:1233-1240 [1993]; Finnerty et al., Oncogene, 8: 2293-2298 [1993])constitute a subfamily of class III receptor tyrosine kinases thatcontain seven extracellular immunoglobulin-like domains and a splitintracellular tyrosine kinase domain. Mustonen and Alitalo, J. Cell.Biol., 129: 895-898 (1995). See also WO 94/10202 published 11 May 1994and PCT/US93/00586 filed 22 Jan. 1993 (Avraham et al.). These threereceptors have 31-36% amino acid identity in their extracellularligand-binding domains.

Mice deficient in Flt1 (Fong et al., Nature, 376: 66-70 [1995]) or Flk1(Shalaby et al., Nature, 376: 62-66 [1995]) (generated by gene targetingin embryonic stem cells) have severe defects in vasculogenesis and diein utero at embryonic day 8-9. The phenotype of the receptor-deficientmice differs considerably, however. Mice lacking Flt1 have adisorganized vascular endothelium that extends to the major vessels aswell as to the microvasculature, while endothelial cell differentiationappears to be normal. Fong et al., supra. Mice lacking Flk1 have a majordefect in the development of mature endothelial cells as well as asevere reduction in hematopoietic cell progenitors. Shalaby et al.,supra. Thus, VEGF may act on endothelial cells at more than one stage ofvasculogenesis.

Flt4 is also specifically expressed in endothelial cells; it is firstobserved in day 8.5 mouse embryos in endothelial cell precursors.Kaipainen et al., Proc. Natl. Acad. Sci. USA, 92: 3566-3570 (1995);Kaipainen et al., J. Exp. Med., 178: 2077-2088 (1993). See also Hatva etal., Am J. Pathol., 146: 368-378 (1995). As development proceeds, Flt4expression becomes confined to the venous and lymphatic endothelium andis finally restricted to the lymphatic vessels. Consistent with thisfinding, adult human tissues show Flt4 expression in lymphaticendothelia while there is a lack of expression in arteries, veins, andcapillaries. Kaipainen et al., Proc. Natl. Acad. Sci. USA, supra. Clonesencoding human and mouse Flt4 have been isolated either by PCR withprimers from conserved tyrosine kinase regions (Finnerty et al., supra;PCT/US93/00586, supra; Aprelikova et al., Cancer Res., 52: 746-748[1992]) or by low-stringency hybridization with a Flk2 probe. Galland etal., Genomics, 13: 475-478 (1992). Alternative splicing of the Flt4 mRNAproduces two variants of the protein differing by 65 amino acids at theC-terminus. Pajusola et al., Oncogene, 8: 2931-2937 (1993). Thesevariants migrate as bands of 170-190 kDa that are partially cleavedproteolytically in the extracellular domain to produce a form of about125 kDa. Pajusola et al., Oncogene, 8, supra; Pajusola et al., Oncogene,9: 3545-3555 (1994). Expression of the longer spliced form of Flt4 as achimera with the extracellular domain of the CSF-1 receptor shows thatthe Flt4 intracellular domain can signal a ligand-dependent growthresponse in rodent fibroblasts. Pajusola et al., Oncogene, 9, supra;Borg et al., Oncogene, 10: 973-984 (1995). Flt4 has been localized tohuman chromosome 5q34-q35 (Aprelikova et al., supra; Galland et al.,Genomics, supra); Flt1 and Flk1 are located at 13q12 (Imbert et al.,Cytogenet. Cell Genet., 67: 175-177 [1994]) and 4q12. Sait et al.,Cytogenet. Cell Genet., 70: 145-146 (1995); Spritz et al., Genomics, 22:431-436 (1994).

VEGF is a homodimeric, cysteine-rich protein that can occur in at leastfour forms due to alternative splicing of its mRNA. Ferrara et al.,supra. While VEGF is a high-affinity ligand for Flt1 and Flk1, it doesnot bind or activate Flt4. Pajusola et al., Oncogene, 9, supra. The onlyother closely related member of the VEGF family is placental growthfactor (PlGF), which has 47% amino acid identity with VEGF. Maglione etal., Proc. Natl. Acad. Sci. USA, 88: 9267-9271 (1991). PlGF also occursin two alternatively spliced forms which differ in the presence orabsence of a basic heparin binding domain of 21 amino acids. Maglione etal., Oncogene, 8: 925-931 (1993); Hauser and Weich, Growth Factors, 9:259-268 (1993). PlGF binds to Flt1 but not to Flk1 (Park et al., J.Biol. Chem., 269: 25646-25654 [1994]); it is believed that its bindingto Flt4 has not been determined. PlGF fails to duplicate the capillaryendothelial cell mitogenesis or vascular permeability activities ofVEGF, suggesting that these activities are mediated by the Flk1receptor. Park et al., supra.

Molecules that modulate the Flk1 receptor or neutralize activation of aVEGF receptor are disclosed in the patent literature. For example, WO95/21613 published 17 Aug. 1995 discloses compounds that modulateKDR/Flk1 receptor signal transduction so as to regulate and/or modulatevasculogenesis and angiogenesis and disclose using Flk1 to evaluate andscreen for drugs and analogs of VEGF involved in Flk1 modulation byeither agonist or antagonist activities; WO 95/21865 published 17 Aug.1995 discloses molecules immunointeractive with animal neuroepithelialkinase (NYK)/Flk1, which molecules can be used to provide agents fortreatment, prophylaxis, and diagnosis of an angiogenic-dependentphenotype; and WO 95/21868 published 17 Aug. 1995 discloses monoclonalantibodies that specifically bind to an extracellular domain of a VEGFreceptor and neutralize activation of the receptor.

SUMMARY OF THE INVENTION

cDNA clones have now been identified that encode a novel protein,designated VRP, which binds to and stimulates the phosphorylation of thereceptor tyrosine kinase Flt4. VRP is related in amino acid sequence toVEGF, but does not interact appreciably with the VEGF receptors, Flt1and Flk1.

In one aspect, the invention provides isolated biologically active humanVRP containing at least 265 amino acids. In another aspect, theinvention supplies isolated biologically active human VEGF-relatedprotein (VRP) comprising an amino acid sequence comprising at leastresidues +1 through 29, inclusive, of FIG. 1. In further aspect, theinvention supplies isolated biologically active human VRP comprising anamino acid sequence shown as residues −20 through 399, inclusive, orresidues 1 through 399, inclusive, of FIG. 1.

The invention also pertains to chimeras comprising the VRP fused toanother polypeptide. For example, the invention provides a chimericpolypeptide comprising the VRP fused to a tag polypeptide sequence. Anexample of such a chimera is epitope-tagged VRP.

In another aspect, the invention provides a composition comprisingbiologically active VRP and a pharmaceutically acceptable carrier. In amore specific embodiment, the invention provides a pharmaceuticalcomposition useful for promotion of vascular or lymph endothelial cellgrowth comprising a therapeutically effective amount of the VRP in apharmaceutically acceptable carrier. In another aspect, this compositionfurther comprises another cell growth factor such as VEGF and/or PDGF.

In a further aspect, the invention provides a method of treatingvascular tissue and promoting angiogenesis in a mammal comprisingadministering to the mammal an effective amount of the compositioncomprising VRP. In another embodiment, the invention provides a methodfor treating trauma affecting the vascular endothelium comprisingadministering to a mammal suffering from said trauma an effective amountof the composition containing the VRP. The trauma is, for example,diabetic ulcers or a wound of the blood vessels or heart. In anotherembodiment, the invention provides a method for treating a dysfunctionalstate characterized by lack of activation or lack of inhibition of areceptor for VRP in a mammal comprising administering to the mammal aneffective amount of the composition containing the VRP.

The invention also provides a method which involves contacting the Flt4receptor with the VRP to cause phosphorylation of the kinase domainthereof. For example, the invention provides a method for stimulatingthe phosphorylation of a tyrosine kinase domain of a Flt4 receptorcomprising contacting an extracellular domain of the Flt4 receptor withthe VRP.

The invention also provides a monoclonal antibody which binds to the VRPand preferably also neutralizes a biological activity of the protein,one biological activity being characterized as promotingneovascularization or vascular permeability or vascular endothelial cellgrowth in a mammal. Alternatively or conjunctively, the inventionprovides a monoclonal antibody which binds to the N-terminal portionfrom residues −20 through 137, inclusive, or from residues +1 through137, inclusive, of the amino acid sequence shown in FIG. 1. The antibodycan be used, for example, to detect the presence of the VRP in abiological sample suspected of having the protein, or to treat patients.The invention contemplates a pharmaceutical composition comprising suchantibody and a pharmaceutically acceptable carrier, as well as a methodof treating diseases or disorders characterized by undesirable excessiveneovascularization or vascular permeability in a mammal comprisingadministering to said mammal an effective amount of one of theantibodies described above. Further included by the invention is amethod for treating a dysfunctional state characterized by excessiveactivation or inhibition of a receptor for VRP in a mammal comprisingadministering to the mammal an effective amount of one of the antibodiesdescribed above.

In addition, the invention contemplates a peptide consisting of an aminoacid sequence shown as residues −20 through −1, inclusive, of FIG. 1.

In a further embodiment, the invention provides an isolated nucleic acidmolecule encoding VRP or a VRP chimera. In one aspect, the nucleic acidmolecule is RNA or DNA that encodes a biologically active VRP or iscomplementary to nucleic acid sequence encoding such VRP, and remainsstably bound to it under stringent conditions. The nucleic acid moleculeoptionally includes the regions of the nucleic acid sequences of FIG. 1which encode signal sequences. In one embodiment, the nucleic acidsequence is selected from:

(a) the coding region of the nucleic acid sequence of FIG. 1 that codesfor the preprotein from residue −20 to residue 399 or that codes for themature protein from residue 1 to residue 399 (i.e., nucleotides 372through 1628, inclusive, or nucleotides 432 through 1628, inclusive, ofthe nucleic acid sequence shown in FIG. 1 as SEQ ID NO: 1); or

(b) a sequence corresponding to the sequence of (a) within the scope ofdegeneracy of the genetic code. In another aspect, the nucleic acidmolecule can be provided in a replicable vector comprising the nucleicacid molecule operably linked to control sequences recognized by a hostcell transfected or transformed with the vector. The invention furtherprovides a host cell comprising the vector or the nucleic acid molecule.A method of producing VRP is also provided which comprises culturing ahost cell comprising the nucleic acid molecule and recovering theprotein from the host cell culture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D depict the nucleotide coding sequence (SEQ ID NO: 1),nucleotide complementary sequence (SEQ ID NO: 2), and deduced amino acidsequence (SEQ ID NO: 3) of the human VRP described herein.

FIG. 2 depicts binding of Flt4/IgG and of Rse/IgG (an unrelated receptorfusion protein) to the human glioma cell line G61, which binding wasevaluated by FACS analysis.

FIGS. 3A and 3B respectively depict a map of cDNA clones encoding humanVRP and an alignment of the protein sequence VRP (SEQ ID NO: 3) withthat of VEGF₁₂₁ (SEQ ID NO: 4) and PlGF₁₃₁ (SEQ ID NO: 5). FIG. 3A showsthe extent of four VRP cDNA clones; dashed lines indicate the missingportions of VH1.1 and VH1.3. Arrows indicate restriction enzyme sites;the shaded box indicates the putative secretion signal sequence; theopen box indicates the mature protein; Y-type designations within theopen box indicate the potential N-linked glycosylation sites; andvertical lines indicate the cysteine residues. A diagram of VEGF₁₂₁ isshown for comparison. The hydropathy plot (Kyle and Doolittle, J. Mol.Biol., 157: 105-132 [1982]) is for VRP. In FIG. 3B, overlining indicatesthe region encoded by an expressed sequence tag (EST) (sequence of aportion of a cDNA clone) from GenBank designated HSC1WF111.

FIG. 4 depicts a map of the cDNA clone for full-length human VRP hereinversus eleven known EST's. The eleven EST partial amino acid sequencefragments are H07991 and H07899 (5′ and 3′ ends of the same clonedfragment, respectively), H05134 and H05177 (3′ and 5′ ends of the samecloned fragment, respectively), HSC1WF112 and HSC1WF111 (3′ and 5′ endsof the same cloned fragment, respectively), T81481 and T81690 (3′ and 5′ends of the same cloned fragment, respectively), R77495 (a 3′ end of acloned fragment), and T84377 and T89295 (5′ and 3′ ends of the samecloned fragment, respectively).

FIG. 5 depicts binding of ¹²⁵I-Flt4/IgG to purified VRP. The binding wasperformed in the absence (−) or presence (+) of 100 nM receptor IgGfusion protein (FIG. 5A) or with increasing concentrations of Flt4/IgG(FIG. 5B).

FIG. 6 shows a graph of the cell count of human lung microvascularendothelial cells as a function of the concentration of VEGF or VRP inthe cell culture medium to assess and compare mitogenic activity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Definitions

In describing the present invention, the following terms will beemployed, and are intended to be defined as indicated below.

“Human VRP” is defined herein to be a polypeptide sequence containing atleast residues −20 to 399, inclusive, or residues +1 to 399, inclusive,of the amino acid sequence shown in FIG. 1, including residues −5 to399, inclusive, and residues −4 to 399, inclusive, of the amino acidsequence shown in FIG. 1, as well as biologically active deletional,insertional, or substitutional variants of the above sequences having atleast 265 amino acids and/or having at least residues +1 through 29,inclusive, of FIG. 1. In a preferred embodiment, the protein sequencehas at least residues +1 through 137, inclusive, of FIG. 1, morepreferably at least residues −20 through 29, inclusive, of FIG. 1, andmost preferably at least residues −20 through 137, inclusive, of FIG. 1.In another preferred embodiment, the biologically active variants have alength of 265 to about 450 amino acid residues, more preferably about300-450, even more preferably about 350-450, and most preferably about399-419 amino acid residues. Another preferred set of variants arevariants that are insertional or substitutional variants, or deletionalvariants where the deletion is in the signal sequence and/or is not inthe N-terminal region of the molecule (i.e., residues 1-29, preferablyresidues 1-137). The definition of VRP excludes all known EST sequences,such as, e.g., H07991, H05134, H05177, HSC1WF112, HSC1WF111, T81481,R77495, H07899, T84377, T81690, and T89295, as well as all forms of VEGFand PlGF.

“Biologically active” for the purposes herein means having the abilityto bind to, and stimulate the phosphorylation of, the Flt4 receptor.Generally, the protein will bind to the extracellular domain of the Flt4receptor and thereby activate or inhibit the intracellular tyrosinekinase domain thereof. Consequently, binding of the protein to thereceptor may result in enhancement or inhibition of proliferation and/ordifferentiation and/or activation of cells having the Flt4 receptor forthe VRP in vivo or in vitro. Binding of the protein to the Flt4 receptorcan be determined using conventional techniques, including competitivebinding methods, such as RIAs, ELISAs, and other competitive bindingassays. Ligand/receptor complexes can be identified using suchseparation methods as filtration, centrifugation, flow cytometry (see,e.g., Lyman et al., Cell, 75:1157-1167 [1993]; Urdal et al., J. Biol.Chem., 263:2870-2877 [1988]; and Gearing et al., EMBO J., 8:3667-3676[1989]), and the like. Results from binding studies can be analyzedusing any conventional graphical representation of the binding data,such as Scatchard analysis (Scatchard, Ann. NY Acad. Sci., 51:660-672[1949]; Goodwin et al., Cell, 73:447-456 [1993]), and the like. Sincethe VRP induces phosphorylation of the Flt4 receptor, conventionaltyrosine phosphorylation assays, such as the assay described in Example5 herein, can also be used as an indication of the formation of a Flt4receptor/VRP complex.

The term “epitope tagged” when used herein refers to a chimericpolypeptide comprising the entire VRP, or a portion thereof, fused to a“tag polypeptide”. The tag polypeptide has enough residues to provide anepitope against which an antibody thereagainst can be made, yet is shortenough such that it does not interfere with activity of the VRP. The tagpolypeptide preferably also is fairly unique so that the antibodythereagainst does not substantially cross-react with other epitopes.Suitable tag polypeptides generally have at least six amino acidresidues and usually between about 8-50 amino acid residues (preferablybetween about 9-30 residues).

“Isolated,” when used to describe the various proteins disclosed herein,means protein that has been identified and separated and/or recoveredfrom a component of its natural environment. Contaminant components ofits natural environment are materials that would interfere withdiagnostic or therapeutic uses for the protein, and may include enzymes,hormones, and other proteinaceous or non-proteinaceous solutes. Inpreferred embodiments, the protein will be purified (1) to a degreesufficient to obtain at least 15 residues of N-terminal or internalamino acid sequence by use of a spinning cup sequenator, or (2) tohomogeneity by SDS-PAGE under non-reducing or reducing conditions usingCoomassie blue or, preferably, silver stain. Isolated protein includesprotein in situ within recombinant cells, since at least one componentof the VRP natural environment will not be present. Ordinarily, however,isolated protein will be prepared by at least one purification step.

“Essentially pure” protein means a composition comprising at least about90% by weight of the protein, based on total weight of the composition,preferably at least about 95% by weight. “Essentially homogeneous”protein means a composition comprising at least about 99% by weight ofprotein, based on total weight of the composition.

An “isolated” VRP nucleic acid molecule is a nucleic acid molecule thatis identified and separated from at least one contaminant nucleic acidmolecule with which it is ordinarily associated in the natural source ofthe VRP nucleic acid. An isolated VRP nucleic acid molecule is otherthan in the form or setting in which it is found in nature. Isolated VRPnucleic acid molecules therefore are distinguished from the VRP nucleicacid molecule as it exists in natural cells. However, an isolated VRPnucleic acid molecule includes VRP nucleic acid molecules contained incells that ordinarily express VRP where, for example, the nucleic acidmolecule is in a chromosomal location different from that of naturalcells.

The isolated VRP polypeptide, VRP nucleic acid, or VRP antibody may belabeled for diagnostic and probe purposes, using a label as describedand defined further below in the discussion on uses of VRP antibodies.

The expression “control sequences” refers to DNA sequences necessary forthe expression of an operably linked coding sequence in a particularhost organism. The control sequences that are suitable for prokaryotes,for example, include a promoter, optionally an operator sequence, aribosome binding site, and possibly, other as yet poorly understoodsequences. Eukaryotic cells are known to utilize promoters,polyadenylation signals, and enhancers.

Nucleic acid is “operably linked” when it is placed into a functionalrelationship with another nucleic acid sequence. For example, DNA for apresequence or secretory leader is operably linked to DNA for apolypeptide if it is expressed as a preprotein that participates in thesecretion of the polypeptide; a promoter or enhancer is operably linkedto a coding sequence if it affects the transcription of the sequence; ora ribosome binding site is operably linked to a coding sequence if it ispositioned so as to facilitate translation. Generally, “operably linked”means that the DNA sequences being linked are contiguous, and, in thecase of a secretory leader, contiguous and in reading phase. However,enhancers do not have to be contiguous. Linking is accomplished byligation at convenient restriction sites. If such sites do not exist,the synthetic oligonucleotide adaptors or linkers are used in accordancewith conventional practice.

The term “antibody” is used in the broadest sense and specificallycovers single anti-VRP monoclonal antibodies (including agonist andantagonist antibodies) and anti-VRP antibody compositions withpolyepitopic specificity.

The term “monoclonal antibody” as used herein refers to an antibodyobtained from a population of substantially homogeneous antibodies,i.e., the individual antibodies comprising the population are identicalexcept for possible naturally-occurring mutations that may be present inminor amounts. Monoclonal antibodies are highly specific, being directedagainst a single antigenic site. Furthermore, in contrast toconventional (polyclonal) antibody preparations which typically includedifferent antibodies directed against different determinants (epitopes),each monoclonal antibody is directed against a single determinant on theantigen.

The monoclonal antibodies herein include hybrid and recombinantantibodies produced by splicing a variable (including hypervariable)domain of an anti-VRP antibody with a constant domain (e.g. “humanized”antibodies), or a light chain with a heavy chain, or a chain from onespecies with a chain from another species, or fusions with heterologousproteins, regardless of species of origin or immunoglobulin class orsubclass designation, as well as antibody fragments (e.g., Fab, F(ab′)₂,and Fv), so long as they exhibit the desired biological activity. See,e.g. U.S. Pat. No. 4,816,567 and Mage and Lamoyi, in Monoclonal AntibodyProduction Techniques and Applications, pp. 79-97 (Marcel Dekker, Inc.:New York, 1987).

Thus, the modifier “monoclonal” indicates the character of the antibodyas being obtained from a substantially homogeneous population ofantibodies, and is not to be construed as requiring production of theantibody by any particular method. For example, the monoclonalantibodies to be used in accordance with the present invention may bemade by the hybridoma method first described by Kohler and Milstein,Nature, 256:495 (1975), or may be made by recombinant DNA methods. U.S.Pat. No. 4,816,567. The “monoclonal antibodies” may also be isolatedfrom phage libraries generated using the techniques described inMcCafferty et al., Nature, 348:552-554 (1990), for example.

“Humanized” forms of non-human (e.g. murine) antibodies are specificchimeric immunoglobulins, immunoglobulin chains, or fragments thereof(such as Fv, Fab, Fab′, F(ab′)₂ or other antigen-binding subsequences ofantibodies) which contain minimal sequence derived from non-humanimmunoglobulin. For the most part, humanized antibodies are humanimmunoglobulins (recipient antibody) in which residues from acomplementary determining region (CDR) of the recipient are replaced byresidues from a CDR of a non-human species (donor antibody) such asmouse, rat, or rabbit having the desired specificity, affinity, andcapacity. In some instances, Fv framework region (FR) residues of thehuman immunoglobulin are replaced by corresponding non-human residues.Furthermore, the humanized antibody may comprise residues which arefound neither in the recipient antibody nor in the imported CDR orframework sequences. These modifications are made to further refine andoptimize antibody performance. In general, the humanized antibody willcomprise substantially all of at least one, and typically two, variabledomains, in which all or substantially all of the CDR regions correspondto those of a non-human immunoglobulin and all or substantially all ofthe FR regions are those of a human immunoglobulin consensus sequence.The humanized antibody optimally also will comprise at least a portionof an immunoglobulin constant region (Fc), typically that of a humanimmunoglobulin.

As used herein, “vascular endothelial cell growth factor,” or “VEGF,”refers to a mammalian growth factor derived originally from bovinepituitary follicular cells having the amino acid sequence of FIG. 2 ofWO 90/13649, and has the human amino acid sequence of FIG. 10 of WO90/13649. See also U.S. Pat. No. 5,194,596, which discloses bovine VEGFof 120 amino acids and human VEGF of 121 amino acids. The biologicalactivity of native VEGF is capable of promoting selective growth ofvascular endothelial cells but not of bovine corneal endothelial cells,lens epithelial cells, adrenal cortex cells, BHK-21 fibroblasts, orkeratinocytes.

The expression “trauma affecting the vascular endothelium” refers totrauma, such as injuries, to the blood vessels or heart, including thevascular network of organs, to which an animal or human, preferably amammal, and most preferably a human, is subjected. Examples of suchtrauma include wounds, incisions, and ulcers, most preferably diabeticulcers and wounds or lacerations of the blood vessels or heart. Traumaincludes conditions caused by internal events as well as those that areimposed by an extrinsic agent such as a pathogen, which can be improvedby promotion of vascular endothelial cell growth. It also refers to thetreatment of wounds in which neovascularization or re-endothelializationis required for healing.

“Promotion of vascular or lymph endothelial cell growth” refers toinducing or increasing the growth of vascular or lymph endothelialcells, including human lung microvascular endothelial cells.

“Disorders related to vasculogenesis and angiogenesis” include cancer,diabetes, hemangioma, and Kaposi's sarcoma.

“Diseases or disorders characterized by undesirable excessiveneovascularization or vascular permeability” refer to diseases ordisorders that include, by way of example, excessive neovascularization,tumors, and especially solid malignant tumors, rheumatoid arthritis,psoriasis, atherosclerosis, diabetic and other retinopathies,retrolental fibroplasia, age-related macular degeneration, neovascularglaucoma, hemangiomas, thyroid hyperplasias (including Grave's disease),corneal and other tissue transplantation, and chronic inflammation.Examples of diseases or disorders characterized by undesirable excessivevascular permeability include edema associated with brain tumors,ascites associated with malignancies, Meigs' syndrome, lunginflammation, nephrotic syndrome, pericardial effusion (such as thatassociated with pericarditis), and pleural effusion.

“Dysfunctional states characterized by excessive activation orinhibition of a receptor for VRP” (such receptor including Flt4) referto disorders or diseases that would be beneficially treated by providingto a mammal having such a pathological condition an antagonist to VRP,such as a chimera of Flt4 or its extracellular domain (e.g., an IgGfusion with Flt4) or an antibody to VRP.

“Dysfunctional states characterized by lack of activation or lack ofinhibition of a receptor for VRP” (such receptor including Flt4) referto disorders or diseases that would be beneficially treated by providingVRP or a VRP receptor agonist to a mammal with such a pathologicalcondition.

“Treatment” refers to both therapeutic treatment and prophylactic orpreventative measures. Those in need of treatment include those alreadywith the disorder as well as those prone to have the disorder or thosein which the disorder is to be prevented.

“Mammal” for purposes of treatment refers to any animal classified as amammal, including humans, domestic and farm animals, and zoo, sports, orpet animals, such as dogs, horses, cats, cows, etc. Preferably, themammal herein is human.

“Effective amount” or “therapeutically effective amount” of the VRP, VRPcomposition, antibody, or antibody composition is an amount that iseffective either to prevent, lessen the worsening of, alleviate, or curethe treated condition. For example, an effective amount of VRP includesthat amount which is sufficient to enhance the growth of vascularendothelium in vivo or to treat trauma, and an “effective amount” of VRPantibody includes that amount which is sufficient to reduce excessneovascularization and angiogenesis.

II. Modes for Carrying Out the Invention

The present invention is based on the discovery of a novel VRP whichbinds to, and stimulates the phosphorylation of, the Flt4 receptor.

Three approaches were undertaken to identify protein that would bind andstimulate the phosphorylation of the Flt4 receptor. First, thefull-length receptor was stably expressed in 293 cells to establish areceptor tyrosine kinase phosphorylation assay of Flt4 activation. Thisassay was used to screen about 400 cell supernatants and tissueextracts, without positive results.

Second, the extracellular domain of the receptor was expressed as afusion protein with an immunoglobulin Fc domain. By using this fusionprotein (Flt4/IgG) to screen cell lines for membrane-bound ligands byFACS analysis, one positive cell line was identified. The human gliomaline, G61, gave about a 10-fold shift in peak fluorescence intensitythat was specific for Flt4/IgG (FIG. 2). Attempts to expression clonethis putative membrane-bound ligand by the transfection of pools of cDNAclones into COS cells followed by screening with labeled Flt4/IgG gaveno positives from 640 pools of 1000-5000 clones each. Flt4/IgG was alsoused to generate polyclonal antisera and monoclonal antibodies that hadagonistic activity and that were used to develop the Flt4 tyrosinephosphorylation assay as described in Example 5 below.

Third, candidate ligand proteins were tested for their ability to bindto Flt4/IgG or to activate the Flt4 phosphorylation assay. Labeled VEGFfailed to bind to Flt4/IgG, although the expected binding of VEGF toFlt1/IgG or Flk1/IgG was routinely detected. The failure of VEGF to bindor stimulate the phosphorylation of Flt4 has been reported by Pajusolaet al., Oncogene, 9, supra. An additional candidate ligand protein wasfound by use of cloning techniques, details of which are provided inExample 3 below. The human VRP cDNA sequence is depicted in FIG. 1A-1D.The predicted molecular weight of the protein is 44.8 kDa.

A description follows as to how the biologically active human VRP may beprepared.

1. Preparation of VRP

Most of the discussion below pertains to production of VRP by culturingcells transformed with a vector containing VRP nucleic acid andrecovering the polypeptide from the cell culture. It is furtherenvisioned that the VRP of this invention may be produced by homologousrecombination, as provided for in WO 91/06667, published 16 May 1991.

Briefly, this method involves transforming primary human cellscontaining a human VRP-encoding gene with a construct (i.e., vector)comprising an amplifiable gene [such as dihydrofolate reductase (DHFR)or others discussed below] and at least one flanking region of a lengthof at least about 150 bp that is homologous with a DNA sequence at thelocus of the coding region of the VRP gene to provide amplification ofthe VRP gene. The amplifiable gene must be at a site that does notinterfere with expression of the VRP gene. The transformation isconducted such that the construct becomes homologously integrated intothe genome of the primary cells to define an amplifiable region.

Primary cells comprising the construct are then selected for by means ofthe amplifiable gene or other marker present in the construct. Thepresence of the marker gene establishes the presence and integration ofthe construct into the host genome. No further selection of the primarycells need be made, since selection will be made in the second host. Ifdesired, the occurrence of the homologous recombination event can bedetermined by employing PCR and either sequencing the resultingamplified DNA sequences or determining the appropriate length of the PCRfragment when DNA from correct homologous integrants is present andexpanding only those cells containing such fragments. Also if desired,the selected cells may be amplified at this point by stressing the cellswith the appropriate amplifying agent (such as methotrexate if theamplifiable gene is DHFR), so that multiple copies of the target geneare obtained. Preferably, however, the amplification step is notconducted until after the second transformation described below.

After the selection step, DNA portions of the genome, sufficiently largeto include the entire amplifiable region, are isolated from the selectedprimary cells. Secondary mammalian expression host cells are thentransformed with these genomic DNA portions and cloned, and clones areselected that contain the amplifiable region. The amplifiable region isthen amplified by means of an amplifying agent if not already amplifiedin the primary cells. Finally, the secondary expression host cells nowcomprising multiple copies of the amplifiable region containing VRP aregrown so as to express the gene and produce the protein.

A. Isolation of DNA Encoding VRP

The DNA encoding VRP may be obtained from any cDNA library prepared fromtissue believed to possess the VRP mRNA and to express it at adetectable level. Accordingly, human VRP DNA can be convenientlyobtained from a cDNA library prepared from human brain tissue, e.g., aglial cell line. The VRP-encoding gene may also be obtained from agenomic library or by oligonucleotide synthesis.

Libraries are screened with probes (such as antibodies to the VRP oroligonucleotides of about 20-80 bases) designed to identify the gene ofinterest or the protein encoded by it. Screening the cDNA or genomiclibrary with the selected probe may be conducted using standardprocedures as described in chapters 10-12 of Sambrook et al., MolecularCloning: A Laboratory Manual (New York: Cold Spring Harbor LaboratoryPress, 1989). An alternative means to isolate the gene encoding VRP isto use PCR methodology as described in section 14 of Sambrook et al.,supra.

A preferred method of practicing this invention is to use carefullyselected oligonucleotide sequences to screen cDNA libraries from varioushuman tissues, preferably brain cell lines. The oligonucleotidesequences selected as probes should be of sufficient length andsufficiently unambiguous that false positives are minimized.

The oligonucleotide must be labeled such that it can be detected uponhybridization to DNA in the library being screened. The preferred methodof labeling is to use ³²P-labeled ATP with polynucleotide kinase, as iswell known in the art, to radiolabel the oligonucleotide. However, othermethods may be used to label the oligonucleotide, including, but notlimited to, biotinylation or enzyme labeling.

In some preferred embodiments, the nucleic acid sequence includes thenative VRP signal sequence. Nucleic acid having all the protein codingsequence is obtained by screening selected cDNA or genomic librariesusing the deduced amino acid sequence disclosed herein for the firsttime, and, if necessary, using conventional primer extension proceduresas described in section 7.79 of Sambrook et al., supra, to detectprecursors and processing intermediates of mRNA that may not have beenreverse-transcribed into cDNA.

Amino acid sequence variants of VRP are prepared by introducingappropriate nucleotide changes into the VRP DNA, or by synthesis of thedesired VRP polypeptide. Such variants represent insertions,substitutions, and/or deletions of, residues within or at one or both ofthe ends of the amino acid sequence shown for the VRP in FIG. 1.Preferably, these variants represent insertions and/or substitutionswithin or at one or both ends of the mature sequence, and/or insertions,substitutions and/or deletions within or at one or both of the ends ofthe signal sequence for VRP shown in FIG. 1. Any combination ofinsertion, substitution, and/or deletion is made to arrive at the finalconstruct, provided that the final construct possesses the desiredbiological activity as defined herein. The amino acid changes also mayalter post-translational processes of the VRP, such as changing thenumber or position of glycosylation sites, altering the membraneanchoring characteristics, and/or altering the intracellular location ofthe VRP by inserting, deleting, or otherwise affecting the leadersequence of the VRP.

Variations in the native sequence as described above can be made usingany of the techniques and guidelines for conservative andnon-conservative mutations set forth in U.S. Pat. No. 5,364,934. Theseinclude oligonucleotide-mediated (site-directed) mutagenesis, alaninescanning, and PCR mutagenesis. See also, for example, Table I thereinand the discussion surrounding this table for guidance on selectingamino acids to change, add, or delete.

B. Insertion of Nucleic Acid into Replicable Vector

The nucleic acid (e.g., cDNA or genomic DNA) encoding native or variantVRP is inserted into a replicable vector for further cloning(amplification of the DNA) or for expression. Many vectors areavailable. The vector components generally include, but are not limitedto, one or more of the following: a signal sequence, an origin ofreplication, one or more marker genes, an enhancer element, a promoter,and a transcription termination sequence.

(i) Signal Sequence Component

The VRPs of this invention may be produced recombinantly not onlydirectly, but also as a fusion polypeptide with a heterologouspolypeptide, which is preferably a signal sequence or other polypeptidehaving a specific cleavage site at the N-terminus of the mature proteinor polypeptide. In general, the signal sequence may be a component ofthe vector, or it may be a part of the VRP DNA that is inserted into thevector. The heterologous signal sequence selected preferably is one thatis recognized and processed (i.e., cleaved by a signal peptidase) by thehost cell. For prokaryotic host cells that do not recognize and processthe native VRP signal sequence, the signal sequence is substituted by aprokaryotic signal sequence selected, for example, from the group of thealkaline phosphatase, penicillinase, 1 pp, or heat-stable enterotoxin IIleaders. For yeast secretion the native signal sequence may besubstituted by, e.g., the yeast invertase leader, alpha factor leader(including Saccharomyces and Kluyveromyces α-factor leaders, the latterdescribed in U.S. Pat. No. 5,010,182 issued 23 Apr. 1991), or acidphosphatase leader, the C. albicans glucoamylase leader (EP 362,179published 4 Apr. 1990), or the signal described in WO 90/13646 published15 Nov. 1990. In mammalian cell expression the native signal sequence(e.g., the VRP presequence that normally directs secretion of VRP fromhuman cells in vivo) is satisfactory, although other mammalian signalsequences may be suitable, such as signal sequences from other animalVRPs, and signal sequences from secreted polypeptides of the same orrelated species, as well as viral secretory leaders, for example, theherpes simplex gD signal.

The DNA for such precursor region is ligated in reading frame to DNAencoding the mature VRP.

(ii) Origin of Replication Component

Both expression and cloning vectors contain a nucleic acid sequence thatenables the vector to replicate in one or more selected host cells.Generally, in cloning vectors this sequence is one that enables thevector to replicate independently of the host chromosomal DNA, andincludes origins of replication or autonomously replicating sequences.Such sequences are well known for a variety of bacteria, yeast, andviruses. The origin of replication from the plasmid pBR322 is suitablefor most Gram-negative bacteria, the 2μ plasmid origin is suitable foryeast, and various viral origins (SV40, polyoma, adenovirus, VSV or BPV)are useful for cloning vectors in mammalian cells. Generally, the originof replication component is not needed for mammalian expression vectors(the SV40 origin may typically be used only because it contains theearly promoter).

Most expression vectors are “shuttle” vectors, i.e., they are capable ofreplication in at least one class of organisms but can be transfectedinto another organism for expression. For example, a vector is cloned inE. coli and then the same vector is transfected into yeast or mammaliancells for expression even though it is not capable of replicatingindependently of the host cell chromosome.

DNA may also be amplified by insertion into the host genome. This isreadily accomplished using Bacillus species as hosts, for example, byincluding in the vector a DNA sequence that is complementary to asequence found in Bacillus genomic DNA. Transfection of Bacillus withthis vector results in homologous recombination with the genome andinsertion of VRP DNA. However, the recovery of genomic DNA encoding VRPis more complex than that of an exogenously replicated vector becauserestriction enzyme digestion is required to excise the VRP DNA.

(iii) Selection Gene Component

Expression and cloning vectors should contain a selection gene, alsotermed a selectable marker. This gene encodes a protein necessary forthe survival or growth of transformed host cells grown in a selectiveculture medium. Host cells not transformed with the vector containingthe selection gene will not survive in the culture medium. Typicalselection genes encode proteins that (a) confer resistance toantibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate,or tetracycline, (b) complement auxotrophic deficiencies, or (c) supplycritical nutrients not available from complex media, e.g., the geneencoding D-alanine racemase for Bacilli.

One example of a selection scheme utilizes a drug to arrest growth of ahost cell. Those cells that are successfully transformed with aheterologous gene produce a protein conferring drug resistance and thussurvive the selection regimen. Examples of such dominant selection usethe drugs neomycin (Southern et al., J. Molec. Appl. Genet., 1:327[1982]), mycophenolic acid (Mulligan et al., Science, 209:1422 [1980])or hygromycin. Sugden et al., Mol. Cell. Biol., 5:410-413 (1985). Thethree examples given above employ bacterial genes under eukaryoticcontrol to convey resistance to the appropriate drug G418 or neomycin(geneticin), xgpt (mycophenolic acid), or hygromycin, respectively.

Another example of suitable selectable markers for mammalian cells arethose that enable the identification of cells competent to take up theVRP nucleic acid, such as DHFR or thymidine kinase. The mammalian celltransformants are placed under selection pressure that only thetransformants are uniquely adapted to survive by virtue of having takenup the marker. Selection pressure is imposed by culturing thetransformants under conditions in which the concentration of selectionagent in the medium is successively changed, thereby leading toamplification of both the selection gene and the DNA that encodes VRP.Amplification is the process by which genes in greater demand for theproduction of a protein critical for growth are reiterated in tandemwithin the chromosomes of successive generations of recombinant cells.Increased quantities of VRP are synthesized from the amplified DNA.Other examples of amplifiable genes include metallothionein-I and -II,preferably primate metallothionein genes, adenosine deaminase, ornithinedecarboxylase, etc.

For example, cells transformed with the DHFR selection gene are firstidentified by culturing all of the transformants in a culture mediumthat contains methotrexate (Mtx), a competitive antagonist of DHFR. Anappropriate host cell when wild-type DHFR is employed is the Chinesehamster ovary (CHO) cell line deficient in DHFR activity, prepared andpropagated as described by Urlaub and Chasin, Proc. Natl. Acad. Sci.USA, 77:4216 (1980). The transformed cells are then exposed to increasedlevels of methotrexate. This leads to the synthesis of multiple copiesof the DHFR gene, and, concomitantly, multiple copies of other DNAcomprising the expression vectors, such as the DNA encoding VRP. Thisamplification technique can be used with any otherwise suitable host,e.g., ATCC No. CCL61 CHO-K1, notwithstanding the presence of endogenousDHFR if, for example, a mutant DHFR gene that is highly resistant to Mtxis employed (EP 117,060).

Alternatively, host cells [particularly wild-type hosts that containendogenous DHFR] transformed or co-transformed with DNA sequencesencoding VRP, wild-type DHFR protein, and another selectable marker suchas aminoglycoside 3′-phosphotransferase (APH) can be selected by cellgrowth in medium containing a selection agent for the selectable markersuch as an aminoglycosidic antibiotic, e.g., kanamycin, neomycin, orG418. See U.S. Pat. No. 4,965,199.

A suitable selection gene for use in yeast is the trp1 gene present inthe yeast plasmid YRp7. Stinchcomb et al., Nature, 282:39 (1979);Kingsman et al., Gene 7:141 (1979); Tschemper et al., Gene 10:157(1980). The trp1 gene provides a selection marker for a mutant strain ofyeast lacking the ability to grow in tryptophan, for example, ATCC No.44076 or PEP4-1. Jones, Genetics, 85:12 (1977). The presence of the trp1lesion in the yeast host cell genome then provides an effectiveenvironment for detecting transformation by growth in the absence oftryptophan. Similarly, Leu2-deficient yeast strains (ATCC 20,622 or38,626) are complemented by known plasmids bearing the Leu2 gene.

In addition, vectors derived from the 1.6 μm circular plasmid pKD1 canbe used for transformation of Kluyveromyces yeasts. Bianchi et al.,Curr. Genet., 12:185 (1987). More recently, an expression system forlarge-scale production of recombinant calf chymosin was reported for K.lactis. Van den Berg, Bio/Technology, 8:135 (1990). Stable multi-copyexpression vectors for secretion of mature recombinant human serumalbumin by industrial strains of Kluyveromyces have also been disclosed.Fleer et al., Bio/Technology, 9:968-975 (1991).

(iv) Promoter Component

Expression and cloning vectors usually contain a promoter that isrecognized by the host organism and is operably linked to the VRPnucleic acid. Promoters are untranslated sequences located upstream (5′)to the start codon of a structural gene (generally within about 100 to1000 bp) that control the transcription and translation of particularnucleic acid sequence, such as the VRP nucleic acid sequence, to whichthey are operably linked. Such promoters typically fall into twoclasses, inducible and constitutive. Inducible promoters are promotersthat initiate increased levels of transcription from DNA under theircontrol in response to some change in culture conditions, e.g., thepresence or absence of a nutrient or a change in temperature. At thistime a large number of promoters recognized by a variety of potentialhost cells are well known. These promoters are operably linked toVRP-encoding DNA by removing the promoter from the source DNA byrestriction enzyme digestion and inserting the isolated promotersequence into the vector. Both the native VRP promoter sequence and manyheterologous promoters may be used to direct amplification and/orexpression of the VRP DNA. However, heterologous promoters arepreferred, as they generally permit greater transcription and higheryields of VRP as compared to the native VRP promoter.

Promoters suitable for use with prokaryotic hosts include theβ-lactamase and lactose promoter systems (Chang et al., Nature, 275:615[1978]; Goeddel et al., Nature, 281:544 [1979]), alkaline phosphatase, atryptophan (trp) promoter system (Goeddel, Nucleic Acids Res., 8:4057[1980]; EP 36,776), and hybrid promoters such as the tac promoter.deBoer et al., Proc. Natl. Acad. Sci. USA, 80:21-25 (1983). However,other known bacterial promoters are suitable. Their nucleotide sequenceshave been published, thereby enabling a skilled worker operably toligate them to DNA encoding VRP (Siebenlist et al, Cell 20:269 [1980])using linkers or adaptors to supply any required restriction sites.Promoters for use in bacterial systems also will contain aShine-Dalgarno (S.D.) sequence operably linked to the DNA encoding VRP.

Promoter sequences are known for eukaryotes. Virtually all eukaryoticgenes have an AT-rich region located approximately 25 to 30 basesupstream from the site where transcription is initiated. Anothersequence found 70 to 80 bases upstream from the start of transcriptionof many genes is a CXCAAT region where X may be any nucleotide. At the3′ end of most eukaryotic genes is an AATAAA sequence that may be thesignal for addition of the poly A tail to the 3′ end of the codingsequence. All of these sequences are suitably inserted into eukaryoticexpression vectors.

Examples of suitable promoting sequences for use with yeast hostsinclude the promoters for 3-phosphoglycerate kinase (Hitzeman et al., J.Biol. Chem., 255:2073 [1980]) or other glycolytic enzymes (Hess et al.,J. Adv. Enzyme Reg., 7:149 [1968]; Holland, Biochemistry, 17:4900[1978]), such as enolase, glyceraldehyde-3-phosphate dehydrogenase,hexokinase, pyruvate decarboxylase, phosphofructokinase,glucose-6-phosphate isomerase, 3-phosphoglycerate mutase, pyruvatekinase, triosephosphate isomerase, phosphoglucose isomerase, andglucokinase.

Other yeast promoters, which are inducible promoters having theadditional advantage of transcription controlled by growth conditions,are the promoter regions for alcohol dehydrogenase 2, isocytochrome C,acid phosphatase, degradative enzymes associated with nitrogenmetabolism, metallothionein, glyceraldehyde-3-phosphate dehydrogenase,and enzymes responsible for maltose and galactose utilization. Suitablevectors and promoters for use in yeast expression are further describedin EP 73,657. Yeast enhancers also are advantageously used with yeastpromoters.

VRP transcription from vectors in mammalian host cells is controlled,for example, by promoters obtained from the genomes of viruses such aspolyoma virus, fowlpox virus (UK 2,211,504 published 5 Jul. 1989),adenovirus (such as Adenovirus 2), bovine papilloma virus, avian sarcomavirus, cytomegalovirus, a retrovirus, hepatitis-B virus and mostpreferably Simian Virus 40 (SV40), from heterologous mammalianpromoters, e.g., the actin promoter or an immunoglobulin promoter, fromheat-shock promoters, and from the promoter normally associated with theVRP sequence, provided such promoters are compatible with the host cellsystems.

The early and late promoters of the SV40 virus are conveniently obtainedas an SV40 restriction fragment that also contains the SV40 viral originof replication. Fiers et al., Nature, 273:113 (1978); Mulligan and Berg,Science, 209:1422-1427 (1980); Pavlakis et al., Proc. Natl. Acad. Sci.USA, 78:7398-7402 (1981). The immediate early promoter of the humancytomegalovirus is conveniently obtained as a HindIII E restrictionfragment. Greenaway et al., Gene, 18:355-360 (1982). A system forexpressing DNA in mammalian hosts using the bovine papilloma virus as avector is disclosed in U.S. Pat. No. 4,419,446. A modification of thissystem is described in U.S. Pat. No. 4,601,978. See also Gray et al.,Nature, 295:503-508 (1982) on expressing cDNA encoding immune interferonin monkey cells; Reyes et al., Nature, 297:598-601 (1982) on expressionof human β-interferon cDNA in mouse cells under the control of athymidine kinase promoter from herpes simplex virus; Canaani and Berg,Proc. Natl. Acad. Sci. USA 79:5166-5170 (1982) on expression of thehuman interferon β1 gene in cultured mouse and rabbit cells; and Gormanet al., Proc. Natl. Acad. Sci. USA, 79:6777-6781 (1982) on expression ofbacterial CAT sequences in CV-1 monkey kidney cells, chicken embryofibroblasts, Chinese hamster ovary cells, HeLa cells, and mouse NIH-3T3cells using the Rous sarcoma virus long terminal repeat as a promoter.

(v) Enhancer Element Component

Transcription of a DNA encoding the VRP of this invention by highereukaryotes is often increased by inserting an enhancer sequence into thevector. Enhancers are cis-acting elements of DNA, usually about from 10to 300 bp, that act on a promoter to increase its transcription.Enhancers are relatively orientation and position independent, havingbeen found 5′ (Laimins et al., Proc. Natl. Acad. Sci. USA, 78:993[1981]) and 3′ (Lusky et al., Mol. Cell Bio., 3:1108 [1983]) to thetranscription unit, within an intron (Banerji et al., Cell, 33:729[1983]), as well as within the coding sequence itself. Osborne et al.,Mol. Cell Bio., 4:1293 (1984). Many enhancer sequences are now knownfrom mammalian genes (globin, elastase, albumin, α-fetoprotein, andinsulin). Typically, however, one will use an enhancer from a eukaryoticcell virus. Examples include the SV40 enhancer on the late side of thereplication origin (bp 100-270), the cytomegalovirus early promoterenhancer, the polyoma enhancer on the late side of the replicationorigin, and adenovirus enhancers. See also Yaniv, Nature, 297:17-18(1982) on enhancing elements for activation of eukaryotic promoters. Theenhancer may be spliced into the vector at a position 5′ or 3′ to theVRP-encoding sequence, but is preferably located at a site 5′ from thepromoter.

(vi) Transcription Termination Component

Expression vectors used in eukaryotic host cells (yeast, fungi, insect,plant, animal, human, or nucleated cells from other multicellularorganisms) will also contain sequences necessary for the termination oftranscription and for stabilizing the mRNA. Such sequences are commonlyavailable from the 5′ and, occasionally 3′, untranslated regions ofeukaryotic or viral DNAs or cDNAs. These regions contain nucleotidesegments transcribed as polyadenylated fragments in the untranslatedportion of the mRNA encoding VRP.

(vii) Construction and Analysis of Vectors

Construction of suitable vectors containing one or more of theabove-listed components employs standard ligation techniques. Isolatedplasmids or DNA fragments are cleaved, tailored, and re-ligated in theform desired to generate the plasmids required.

For analysis to confirm correct sequences in plasmids constructed, theligation mixtures are used to transform E. coli K12 strain 294 (ATCC31,446) and successful transformants selected by ampicillin ortetracycline resistance where appropriate. Plasmids from thetransformants are prepared, analyzed by restriction endonucleasedigestion, and/or sequenced by the method of Messing et al., NucleicAcids Res., 9:309 (1981) or by the method of Maxam et al., Methods inEnzymology, 65:499 (1980).

(viii) Transient Expression Vectors

Particularly useful in the practice of this invention are expressionvectors that provide for the transient expression in mammalian cells ofDNA encoding VRP. In general, transient expression involves the use ofan expression vector that is able to replicate efficiently in a hostcell, such that the host cell accumulates many copies of the expressionvector and, in turn, synthesizes high levels of a desired polypeptideencoded by the expression vector. Sambrook et al., supra, pp.16.17-16.22. Transient expression systems, comprising a suitableexpression vector and a host cell, allow for the convenient positiveidentification of polypeptides encoded by cloned DNAs, as well as forthe rapid screening of such polypeptides for desired biological orphysiological properties. Thus, transient expression systems areparticularly useful in the invention for purposes of identifying analogsand variants of VRP that are biologically active VRP.

(ix) Suitable Exemplary Vertebrate Cell Vectors

Other methods, vectors, and host cells suitable for adaptation to thesynthesis of VRP in recombinant vertebrate cell culture are described inGething et al., Nature, 293:620-625 (1981); Mantei et al., Nature,281:40-46 (1979); EP 117,060; and EP 117,058. A particularly usefulplasmid for mammalian cell culture expression of VRP is pRK5 (EP307,247) or pSVI6B. WO 91/08291 published 13 Jun. 1991.

C. Selection and Transformation of Host Cells

Suitable host cells for cloning or expressing the DNA in the vectorsherein are the prokaryote, yeast, or higher eukaryote cells describedabove. Suitable prokaryotes for this purpose include eubacteria, such asGram-negative or Gram-positive organisms, for example,Enterobacteriaceae such as Escherichia, e.g., E. coli, Enterobacter,Erwinia, Klebsiella, Proteus, Salmonella, e.g., Salmonella typhimurium,Serratia, e.g., Serratia marcescans, and Shigella, as well as Bacillisuch as B. subtilis and B. licheniformis (e.g., B. licheniformis 41Pdisclosed in DD 266,710 published 12 Apr. 1989), Pseudomonas such as P.aeruginosa, and Streptomyces. One preferred E. coli cloning host is E.coli 294 (ATCC 31,446), although other strains such as E. coli B, E.coli X1776 (ATCC 31,537), and E. coli W3110 (ATCC 27,325) are suitable.These examples are illustrative rather than limiting. Strain W3110 is aparticularly preferred host or parent host because it is a common hoststrain for recombinant DNA product fermentations. Preferably, the hostcell should secrete minimal amounts of proteolytic enzymes. For example,strain W3110 may be modified to effect a genetic mutation in the genesencoding proteins, with examples of such hosts including E. coli W3110strain 27C7. The complete genotype of 27C7 is tonAΔ ptr3 phoAΔE15Δ(argF-lac)169 ompTΔ degP41kan^(r). Strain 27C7 was deposited on 30 Oct.1991 in the American Type Culture Collection as ATCC No. 55,244.Alternatively, the strain of E. coli having mutant periplasmic proteasedisclosed in U.S. Pat. No. 4,946,783 issued 7 Aug. 1990 may be employed.Alternatively still, methods of cloning, e.g., PCR or other nucleic acidpolymerase reactions, are suitable.

In addition to prokaryotes, eukaryotic microbes such as filamentousfungi or yeast are suitable cloning or expression hosts for VRP-encodingvectors. Saccharomyces cerevisiae, or common baker's yeast, is the mostcommonly used among lower eukaryotic host microorganisms. However, anumber of other genera, species, and strains are commonly available anduseful herein, such as Schizosaccharomyces pombe (Beach and Nurse,Nature, 290:140 [1981]; EP 139,383 published 2 May 1985); Kluyveromyceshosts (U.S. Pat. No. 4,943,529; Fleer et al., supra) such as, e.g., K.lactis [MW98-8C, CBS683, CBS4574; Louvencourt et al., J. Bacteriol., 737(1983)], K. fragilis (ATCC 12,424), K. bulgaricus (ATCC 16,045), K.wickeramii (ATCC 24,178), K. waltii (ATCC 56,500), K. drosophilarum(ATCC 36,906; Van den Berg et al., supra), K. thermotolerans, and K.marxianus; yarrowia [EP 402,226]; Pichia pastoris (EP 183,070;Sreekrishna et al., J. Basic Microbiol., 28:265-278 [1988]); Candida;Trichoderma reesia (EP 244,234); Neurospora crassa (Case et al., Proc.Natl. Acad. Sci. USA, 76:5259-5263 [1979]); Schwanniomyces such asSchwanniomyces occidentalis (EP 394,538 published 31 Oct. 1990); andfilamentous fungi such as, e.g., Neurospora, Penicillium, Tolypocladium(WO 91/00357 published 10 Jan. 1991), and Aspergillus hosts such as A.nidulans (Ballance et al., Biochem. Biophys. Res. Commun., 112:284-289[1983]; Tilburn et al., Gene, 26:205-221 [1983]; Yelton et al., Proc.Natl. Acad. Sci. USA, 81:1470-1474 [1984]) and A. niger. Kelly andHynes, EMBO J., 4:475-479 (1985).

Suitable host cells for the expression of glycosylated VRP are derivedfrom multicellular organisms. Such host cells are capable of complexprocessing and glycosylation activities. In principle, any highereukaryotic cell culture is workable, whether from vertebrate orinvertebrate culture. Examples of invertebrate cells include plant andinsect cells. Numerous baculoviral strains and variants andcorresponding permissive insect host cells from hosts such as Spodopterafrugiperda (caterpillar), Aedes aegypti (mosquito), Aedes albopictus(mosquito), Drosophila melanogaster (fruitfly), and Bombyx mori havebeen identified. See, e.g., Luckow et al., Bio/Technology, 6:47-55(1988); Miller et al., in Genetic Engineering, Setlow et al., eds., Vol.8 (Plenum Publishing, 1986), pp. 277-279; and Maeda et al., Nature,315:592-594 (1985). A variety of viral strains for transfection arepublicly available, e.g., the L-1 variant of Autographa californica NPVand the Bm-5 strain of Bombyx mori NPV, and such viruses may be used asthe virus herein according to the present invention, particularly fortransfection of Spodoptera frugiperda cells.

Plant cell cultures of cotton, corn, potato, soybean, petunia, tomato,and tobacco can be utilized as hosts. Typically, plant cells aretransfected by incubation with certain strains of the bacteriumAgrobacterium tumefaciens, which has been previously manipulated tocontain the VRP-encoding DNA. During incubation of the plant cellculture with A. tumefaciens, the DNA encoding the VRP is transferred tothe plant cell host such that it is transfected, and will, underappropriate conditions, express the VRP-encoding DNA. In addition,regulatory and signal sequences compatible with plant cells areavailable, such as the nopaline synthase promoter and polyadenylationsignal sequences. Depicker et al., J. Mol. Appl. Gen., 1:561 (1982). Inaddition, DNA segments isolated from the upstream region of the T-DNA780 gene are capable of activating or increasing transcription levels ofplant-expressible genes in recombinant DNA-containing plant tissue. EP321,196 published 21 Jun. 1989.

However, interest has been greatest in vertebrate cells, and propagationof vertebrate cells in culture (tissue culture) has become a routineprocedure. See, e.g., Tissue Culture, Academic Press, Kruse andPatterson, editors (1973). Examples of useful mammalian host cell linesare monkey kidney CV1 line transformed by SV40 (COS-7, ATCC CRL 1651);human embryonic kidney line (293 or 293 cells subcloned for growth insuspension culture, Graham et al., J. Gen Virol., 36:59 [1977]); babyhamster kidney cells (BHK, ATCC CCL 10); Chinese hamster ovarycells/-DHFR (CHO, Urlaub and Chasin, Proc. Natl. Acad. Sci. USA, 77:4216[1980]); mouse sertoli cells (TM4, Mather, Biol. Reprod., 23:243-251[1980]); monkey kidney cells (CV1 ATCC CCL 70); African green monkeykidney cells (VERO-76, ATCC CRL-1587); human cervical carcinoma cells(HELA, ATCC CCL 2); canine kidney cells (MDCK, ATCC CCL 34); buffalo ratliver cells (BRL 3A, ATCC CRL 1442); human lung cells (W138, ATCC CCL75); human liver cells (Hep G2, HB 8065); mouse mammary tumor (MMT060562, ATCC CCL51); TRI cells (Mather et al., Annals N.Y. Acad. Sci.,383:44-68 [1982]); MRC 5 cells; FS4 cells; and a human hepatoma line(Hep G2).

Host cells are transfected and preferably transformed with theabove-described expression or cloning vectors for VRP production andcultured in conventional nutrient media modified as appropriate forinducing promoters, selecting transformants, or amplifying the genesencoding the desired sequences.

Transfection refers to the taking up of an expression vector by a hostcell whether or not any coding sequences are in fact expressed. Numerousmethods of transfection are known to the ordinarily skilled artisan, forexample, CaPO₄ and electroporation. Successful transfection is generallyrecognized when any indication of the operation of this vector occurswithin the host cell.

Transformation means introducing DNA into an organism so that the DNA isreplicable, either as an extrachromosomal element or by chromosomalintegrant. Depending on the host cell used, transformation is done usingstandard techniques appropriate to such cells. The calcium treatmentemploying calcium chloride, as described in section 1.82 of Sambrook etal., supra, or electroporation is generally used for prokaryotes orother cells that contain substantial cell-wall barriers. Infection withAgrobacterium tumefaciens is used for transformation of certain plantcells, as described by Shaw et al., Gene, 23:315 (1983) and WO 89/05859published 29 Jun. 1989. In addition, plants may be transfected usingultrasound treatment as described in WO 91/00358 published 10 Jan. 1991.

For mammalian cells without such cell walls, the calcium phosphateprecipitation method of Graham and van der Eb, Virology, 52:456-457(1978) is preferred. General aspects of mammalian cell host systemtransformations have been described in U.S. Pat. No. 4,399,216 issued 16Aug. 1983. Transformations into yeast are typically carried outaccording to the method of Van Solingen et al., J. Bact., 130:946 (1977)and Hsiao et al., Proc. Natl. Acad. Sci. (USA), 76:3829 (1979). However,other methods for introducing DNA into cells, such as by nuclearmicroinjection, electroporation, bacterial protoplast fusion with intactcells, or polycations, e.g., polybrene, polyornithine, etc., may also beused. For various techniques for transforming mammalian cells, see Keownet al., Methods in Enzymology, 185:527-537 (1990) and Mansour et al.,Nature, 336:348-352 (1988).

D. Culturing the Host Cells

Prokaryotic cells used to produce the VRP polypeptide of this inventionare cultured in suitable media as described generally in Sambrook etal., supra.

The mammalian host cells used to produce the VRP of this invention maybe cultured in a variety of media. Commercially available media such asHam's F10 (Sigma), Minimal Essential Medium ([MEM], Sigma), RPMI-1640(Sigma), and Dulbecco's Modified Eagle's Medium ([DMEM], Sigma) aresuitable for culturing the host cells. In addition, any of the mediadescribed in Ham and Wallace, Meth. Enz., 58:44 (1979), Barnes and Sato,Anal. Biochem.,102:255 (1980), U.S. Pat. Nos. 4,767,704; 4,657,866;4,927,762; 4,560,655; or 5,122,469; WO 90/03430; WO 87/00195; or U.S.Pat. Re. 30,985 may be used as culture media for the host cells. Any ofthese media may be supplemented as necessary with hormones and/or othergrowth factors (such as insulin, transferrin, or epidermal growthfactor), salts (such as sodium chloride, calcium, magnesium, andphosphate), buffers (such as HEPES), nucleosides (such as adenosine andthymidine), antibiotics (such as Gentamycin™ drug), trace elements(defined as inorganic compounds usually present at final concentrationsin the micromolar range), and glucose or an equivalent energy source.Any other necessary supplements may also be included at appropriateconcentrations that would be known to those skilled in the art. Theculture conditions, such as temperature, pH, and the like, are thosepreviously used with the host cell selected for expression, and will beapparent to the ordinarily skilled artisan.

In general, principles, protocols, and practical techniques formaximizing the productivity of mammalian cell cultures can be found inMammalian Cell Biotechnology: a Practical Approach, M. Butler, ed. (IRLPress, 1991).

The host cells referred to in this disclosure encompass cells in cultureas well as cells that are within a host animal.

E. Detecting Gene Amplification/Expression

Gene amplification and/or expression may be measured in a sampledirectly, for example, by conventional Southern blotting, Northernblotting to quantitate the transcription of mRNA (Thomas, Proc. Natl.Acad. Sci. USA, 77:5201-5205 [1980]), dot blotting (DNA analysis), or insitu hybridization, using an appropriately labeled probe, based on thesequences provided herein. Various labels may be employed, most commonlyradioisotopes, particularly ³²P. However, other techniques may also beemployed, such as using biotin-modified nucleotides for introductioninto a polynucleotide. The biotin then serves as the site for binding toavidin or antibodies, which may be labeled with a wide variety oflabels, such as radionuclides, fluorescers, enzymes, or the like.Alternatively, antibodies may be employed that can recognize specificduplexes, including DNA duplexes, RNA duplexes, and DNA-RNA hybridduplexes or DNA-protein duplexes. The antibodies in turn may be labeledand the assay may be carried out where the duplex is bound to a surface,so that upon the formation of duplex on the surface, the presence ofantibody bound to the duplex can be detected.

Gene expression, alternatively, may be measured by immunologicalmethods, such as immunohistochemical staining of tissue sections andassay of cell culture or body fluids, to quantitate directly theexpression of gene product. With immunohistochemical stainingtechniques, a cell sample is prepared, typically by dehydration andfixation, followed by reaction with labeled antibodies specific for thegene product coupled, where the labels are usually visually detectable,such as enzymatic labels, fluorescent labels, luminescent labels, andthe like. A particularly sensitive staining technique suitable for usein the present invention is described by Hsu et al., Am. J. Clin. Path.,75:734-738 (1980).

Antibodies useful for immunohistochemical staining and/or assay ofsample fluids may be either monoclonal or polyclonal, and may beprepared in any mammal. Conveniently, the antibodies may be preparedagainst a native VRP polypeptide or against a synthetic peptide based onthe DNA sequences provided herein as described further in Section 4below.

F. Purification of VRP Polypeptide

VRP preferably is recovered from the culture medium as a secretedpolypeptide, although it also may be recovered from host cell lysateswhen directly produced without a secretory signal. If the VRP ismembrane-bound, it can be released from the membrane using a suitabledetergent solution (e.g. Triton-X 100)

When VRP is produced in a recombinant cell other than one of humanorigin, the VRP is completely free of proteins or polypeptides of humanorigin. However, it is necessary to purify VRP from recombinant cellproteins or polypeptides to obtain preparations that are substantiallyhomogeneous as to VRP. As a first step, the culture medium or lysate iscentrifuged to remove particulate cell debris. VRP thereafter ispurified from contaminant soluble proteins and polypeptides, with thefollowing procedures being exemplary of suitable purificationprocedures: by fractionation on an ion-exchange column; ethanolprecipitation; reverse phase HPLC; chromatography on silica or on acation-exchange resin such as DEAE; chromatofocusing; SDS-PAGE; ammoniumsulfate precipitation; gel filtration using, for example, Sephadex G-75;and protein A Sepharose columns to remove contaminants such as IgG.

In the preferred embodiment, the Flt4 receptor-IgG fusion is immobilizedon an affinity chromatography column and the VRP can be isolated byaffinity purification using this column. Alternatively, the VRP isjoined at its N-terminus to a glycoprotein D sequence and is passedthrough an affinity chromatography column on which is immobilized ananti-gD monoclonal antibody such as 5B6, which is specific for aglycoprotein D sequence.

VRP variants in which residues have been deleted, inserted, orsubstituted are recovered in the same fashion as native VRP, takingaccount of any substantial changes in properties occasioned by thevariation. For example, preparation of a VRP fusion with another proteinor polypeptide, e.g., a bacterial or viral antigen, facilitatespurification; an immunoaffinity column containing antibody to theantigen can be used to adsorb the fusion polypeptide. Immunoaffinitycolumns such as a rabbit polyclonal anti-VRP column can be employed toabsorb the VRP variant by binding it to at least one remaining immuneepitope.

A protease inhibitor such as phenyl methyl sulfonyl fluoride (PMSF) alsomay be useful to inhibit proteolytic degradation during purification,and antibiotics may be included to prevent the growth of adventitiouscontaminants. One skilled in the art will appreciate that purificationmethods suitable for native VRP may require modification to account forchanges in the character of VRP or its variants upon expression inrecombinant cell culture.

G. Covalent Modifications of VRP Polypeptides

Covalent modifications of VRP polypeptides are included within the scopeof this invention. Both native VRP and amino acid sequence variants ofthe VRP may be covalently modified. One type of covalent modification ofthe VRP is introduced into the molecule by reacting targeted amino acidresidues of the VRP with an organic derivatizing agent that is capableof reacting with selected side chains or the N— or C-terminal residuesof the VRP.

Cysteinyl residues most commonly are reacted with α-haloacetates (andcorresponding amines), such as chloroacetic acid or chloroacetamide, togive carboxymethyl or carboxyamidomethyl derivatives. Cysteinyl residuesalso are derivatized by reaction with bromotrifluoroacetone,α-bromo-β-(5-imidozoyl)propionic acid, chloroacetyl phosphate,N-alkylmaleimides, 3-nitro-2-pyridyl disulfide, methyl 2-pyridyldisulfide, p-chloromercuribenzoate, 2-chloromercuri-4-nitrophenol, orchloro-7-nitrobenzo-2-oxa-1,3-diazole.

Histidyl residues are derivatized by reaction with diethylpyrocarbonateat pH 5.5-7.0 because this agent is relatively specific for the histidylside chain. Para-bromophenacyl bromide also is useful; the reaction ispreferably performed in 0. 1M sodium cacodylate at pH 6.0.

Lysinyl and amino terminal residues are reacted with succinic or othercarboxylic acid anhydrides. Derivatization with these agents has theeffect of reversing the charge of the lysinyl residues. Other suitablereagents for derivatizing α-amino-containing residues includeimidoesters such as methyl picolinimidate, pyridoxal phosphate,pyridoxal, chloroborohydride, trinitrobenzenesulfonic acid,O-methylisourea, 2,4-pentanedione, and transaminase-catalyzed reactionwith glyoxylate.

Arginyl residues are modified by reaction with one or severalconventional reagents, among them phenylglyoxal, 2,3-butanedione,1,2-cyclohexanedione, and ninhydrin. Derivatization of arginine residuesrequires that the reaction be performed under alkaline conditionsbecause of the high pK_(a) of the guanidine functional group.Furthermore, these reagents may react with the groups of lysine as wellas with the arginine epsilon-amino group.

The specific modification of tyrosyl residues may be made, withparticular interest in introducing spectral labels into tyrosyl residuesby reaction with aromatic diazonium compounds or tetranitromethane. Mostcommonly, N-acetylimidizole and tetranitromethane are used to formO-acetyl tyrosyl species and 3-nitro derivatives, respectively. Tyrosylresidues are iodinated using ¹²⁵I or ¹³¹I to prepare labeled proteinsfor use in radioimmunoassay, the chloramine T method being suitable.

Carboxyl side groups (aspartyl or glutamyl) are selectively modified byreaction with carbodiimides (R—N═C═N—R′), where R and R′ are differentalkyl groups, such as 1-cyclohexyl-3-(2-morpholinyl-4-ethyl)carbodiimide or 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)carbodiimide.Furthermore, aspartyl and glutamyl residues are converted to asparaginyland glutaminyl residues by reaction with ammonium ions.

Derivatization with bifunctional agents is useful for crosslinking VRPto a water-insoluble support matrix or surface for use in the method forpurifying anti-VRP antibodies, and vice-versa. Commonly usedcrosslinking agents include, e.g., 1,1-bis(diazoacetyl)-2-phenylethane,glutaraldehyde, N-hydroxysuccinimide esters, for example, esters with4-azido-salicylic acid, homobifunctional imidoesters, includingdisuccinimidyl esters such as 3,3′-dithiobis(succinimidylpropionate),and bifunctional maleimides such as bis-N-maleimido-1,8-octane.Derivatizing agents such asmethyl-3-[(p-azidophenyl)dithio]propioimidate yield photoactivatableintermediates that are capable of forming crosslinks in the presence oflight. Alternatively, reactive water-insoluble matrices such as cyanogenbromide-activated carbohydrates and the reactive substrates described inU.S. Pat. Nos. 3,969,287; 3,691,016; 4,195,128; 4,247,642; 4,229,537;and 4,330,440 are employed for protein immobilization.

Glutaminyl and asparaginyl residues are frequently deamidated to thecorresponding glutamyl and aspartyl residues, respectively. Theseresidues are deamidated under neutral or basic conditions. Thedeamidated form of these residues falls within the scope of thisinvention.

Other modifications include hydroxylation of proline and lysine,phosphorylation of hydroxyl groups of seryl or threonyl residues,methylation of the α-amino groups of lysine, arginine, and histidineside chains (T. E. Creighton, Proteins: Structure and MolecularProperties, W.H. Freeman & Co., San Francisco, pp. 79-86 [1983]),acetylation of the N-terminal amine, and amidation of any C-terminalcarboxyl group.

Another type of covalent modification of the VRP polypeptide includedwithin the scope of this invention comprises altering the nativeglycosylation pattern of the polypeptide. By altering is meant deletingone or more carbohydrate moieties found in native VRP, and/or adding oneor more glycosylation sites that are not present in the native VRP.

Glycosylation of polypeptides is typically either N-linked or O-linked.N-linked refers to the attachment of the carbohydrate moiety to the sidechain of an asparagine residue. The tripeptide sequencesasparagine-X-serine and asparagine-X-threonine, where X is any aminoacid except proline, are the recognition sequences for enzymaticattachment of the carbohydrate moiety to the asparagine side chain.Thus, the presence of either of these tripeptide sequences in apolypeptide creates a potential glycosylation site. O-linkedglycosylation refers to the attachment of one of the sugarsN-aceylgalactosamine, galactose, or xylose to a hydroxylamino acid, mostcommonly serine or threonine, although 5-hydroxyproline or5-hydroxylysine may also be used.

Addition of glycosylation sites to the VRP polypeptide is convenientlyaccomplished by altering the amino acid sequence such that it containsone or more of the above-described tripeptide sequences (for N-linkedglycosylation sites). The alteration may also be made by the additionof, or substitution by, one or more serine or threonine residues to thenative VRP sequence (for O-linked glycosylation sites). For ease, theVRP amino acid sequence is preferably altered through changes at the DNAlevel, particularly by mutating the DNA encoding the VRP polypeptide atpreselected bases such that codons are generated that will translateinto the desired amino acids. The DNA mutation(s) may be made usingmethods described above and in U.S. Pat. No. 5,364,934, supra.

Another means of increasing the number of carbohydrate moieties on theVRP polypeptide is by chemical or enzymatic coupling of glycosides tothe polypeptide. These procedures are advantageous in that they do notrequire production of the polypeptide in a host cell that hasglycosylation capabilities for N— or O-linked glycosylation. Dependingon the coupling mode used, the sugar(s) may be attached to (a) arginineand histidine, (b) free carboxyl groups, (c) free sulfhydryl groups suchas those of cysteine, (d) free hydroxyl groups such as those of serine,threonine, or hydroxyproline, (e) aromatic residues such as those ofphenylalanine, tyrosine, or tryptophan, or (f) the amide group ofglutamine. These methods are described in WO 87/05330 published 11 Sep.1987, and in Aplin and Wriston, CRC Crit. Rev. Biochem., pp. 259-306(1981).

Removal of carbohydrate moieties present on the VRP polypeptide may beaccomplished chemically or enzymatically. Chemical deglycosylationrequires exposure of the polypeptide to the compoundtrifluoromethanesulfonic acid, or an equivalent compound. This treatmentresults in the cleavage of most or all sugars except the linking sugar(N-acetylglucosamine or N-acetylgalactosamine), while leaving thepolypeptide intact. Chemical deglycosylation is described by Hakimuddin,et al., Arch. Biochem. Biophys., 259:52 (1987) and by Edge et al., Anal.Biochem., 118:131 (1981). Enzymatic cleavage of carbohydrate moieties onpolypeptides can be achieved by the use of a variety of endo- andexo-glycosidases as described by Thotakura et al., Meth. Enzymol.,138:350 (1987).

Glycosylation at potential glycosylation sites may be prevented by theuse of the compound tunicamycin as described by Duskin et al., J. Biol.Chem., 257:3105 (1982). Tunicamycin blocks the formation ofprotein-N-glycoside linkages.

Another type of covalent modification of VRP comprises linking the VRPpolypeptide to one of a variety of nonproteinaceous polymers, e.g.,polyethylene glycol, polypropylene glycol, or polyoxyalkylenes, in themanner set forth in U.S. Pat. Nos. 4,640,835; 4,496,689; 4,301,144;4,670,417; 4,791,192 or 4,179,337.

Since it is often difficult to predict in advance the characteristics ofa variant VRP, it will be appreciated that some screening of therecovered variant will be needed to select the optimal variant. A changein the immunological character of the VRP molecule, such as affinity fora given antibody, is also able to be measured by a competitive-typeimmunoassay. The variant is assayed for changes in the suppression orenhancement of its mitogenic activity by comparison to the activityobserved for native VRP in the same assay. For example, one can screenfor the ability of the variant VRP to stimulate protein kinase activityof the Flt4 receptor as described in Example 5 herein. Other potentialmodifications of protein or polypeptide properties such as redox orthermal stability, hydrophobicity, susceptibility to proteolyticdegradation, or the tendency to aggregate with carriers or intomultimers are assayed by methods well known in the art.

H. Epitope-Tagged VRP

This invention encompasses chimeric polypeptides comprising VRP fused toanother polypeptide. In one preferred embodiment, the chimericpolypeptide comprises a fusion of the VRP with a tag polypeptide whichprovides an epitope to which an anti-tag antibody can selectively bind.The epitope tag is generally placed at the amino- or carboxyl-terminusof the VRP. Such epitope-tagged forms of the VRP are desirable, as thepresence thereof can be detected using a labeled antibody against thetag polypeptide. Also, provision of the epitope tag enables the VRP tobe readily purified by affinity purification using the anti-tagantibody. Affinity purification techniques and diagnostic assaysinvolving antibodies are described later herein.

Tag polypeptides and their respective antibodies are well known in theart. Examples include the flu HA tag polypeptide and its antibody 12CA5(Field et al., Mol. Cell. Biol., 8:2159-2165 [1988]); the c-myc tag andthe 8F9, 3C7, 6E10, G4, B7 and 9E10 antibodies thereto (Evan et al.,Molecular and Cellular Biology, 5:3610-3616 [1985]); and the HerpesSimplex virus glycoprotein D (gD) tag and its antibody. Paborsky et al.,Protein Engineering, 3(6):547-553 (1990). Other tag polypeptides havebeen disclosed. Examples include the Flag-peptide (Hopp et al.,BioTechnology, 6:1204-1210 [1988]); the KT3 epitope peptide (Martin etal., Science, 255:192-194 [1992]); an α-tubulin epitope peptide (Skinneret al., J. Biol. Chem., 266:15163-15166 [1991]); and the T7 gene 10protein peptide tag. Lutz-Freyermuth et al., Proc. Natl. Acad. Sci. USA,87:6393-6397 (1990). Once the tag polypeptide has been selected, anantibody thereto can be generated using the techniques disclosed herein.

The general methods suitable for the construction and production ofepitope-tagged VRP are the same as those disclosed hereinabove withregard to (native or variant) VRP. VRP-tag polypeptide fusions are mostconveniently constructed by fusing the cDNA sequence encoding the VRPportion in-frame to the tag polypeptide DNA sequence and expressing theresultant DNA fusion construct in appropriate host cells. Ordinarily,when preparing the VRP-tag polypeptide chimeras of the presentinvention, nucleic acid encoding the VRP will be fused at its 3′ end tonucleic acid encoding the N-terminus of the tag polypeptide, however 5′fusions are also possible.

Epitope-tagged VRP can be conveniently purified by affinitychromatography using the anti-tag antibody. The matrix to which theaffinity antibody is attached is most often agarose, but other matricesare available (e.g. controlled pore glass orpoly(styrenedivinyl)benzene). The epitope-tagged VRP can be eluted fromthe affinity column by varying the buffer pH or ionic strength or addingchaotropic agents, for example.

2. Therapeutic Uses, Compositions, and Administration of VRP

VRP is believed to find therapeutic use for treating mammals viastimulation or inhibition of growth and/or differentiation and/oractivation of cells having the Flt4 receptor or one or more other VRPreceptors. Exogenous VRP may be administered to a patient in thesecircumstances. The human VRP is clearly useful insofar as it can beadministered to a human having depressed levels of endogenous VRP,preferably in the situation where such depressed levels lead to apathological disorder, or where there is lack of activation orinhibition of the Flt4 receptor or one or more other VRP receptors.

Various potential therapeutic uses of VRP include those in which VEGF isuseful. Examples of these include uses associated with the vascularendothelium, such as the treatment of traumata to the vascular network,in view of the demonstrated rapid promotion by VEGF of the proliferationof vascular endothelial cells that would surround the traumata and inview of the relationship between VEGF and the VRP established herein.Examples of such traumata that could be so treated include, but are notlimited to, surgical incisions, particularly those involving the heart,wounds, including lacerations, incisions, and penetrations of bloodvessels, and surface ulcers involving the vascular endothelium such asdiabetic, haemophiliac, and varicose ulcers. Other physiologicalconditions that could be improved based on the selective mitogeniccharacter of the VRP are also included herein.

For the traumatic indications referred to above, the VRP molecule willbe formulated and dosed in a fashion consistent with good medicalpractice taking into account the specific disorder to be treated, thecondition of the individual patient, the site of delivery of the VRP,the method of administration, and other factors known to practitioners.

Additional indications for the VRP are in the treatment offull-thickness wounds such as dermal ulcers, including the categories ofpressure sores, venous ulcers, and diabetic ulcers, as well as offull-thickness bums and injuries where angiogenesis is required toprepare the bum or injured site for a skin graft or flap. In this casethe VRP is either applied directly to the site or it is used to soak theskin or flap that is being transplanted prior to grafting. In a similarfashion, the VRP can be used in plastic surgery when reconstruction isrequired following a burn or other trauma, or for cosmetic purposes.

Angiogenesis is also important in keeping wounds clean and non-infected.The VRP can therefore be used in association with general surgery andfollowing the repair of cuts and lacerations. It is particularly usefulin the treatment of abdominal wounds with a high risk of infection.Neovascularization is also key to fracture repair, since blood vesselsdevelop at the site of bone injury. Administration of the VRP to thesite of a fracture is therefore another utility.

In cases where the VRP is being used for topical wound healing, asdescribed above, it may be administered by any of the routes describedbelow for the re-endothelialization of vascular tissue, or morepreferably by topical means. In these cases, it will be administered aseither a solution, spray, gel, cream, ointment, or dry powder directlyto the site of injury. Slow-release devices directing the VRP to theinjured site will also be used. In topical applications, the VRP will beapplied at a concentration ranging from about 50 to 1,000 μg/mL, eitherin a single application, or in dosing regimens that are daily or everyfew days for a period of one week to several weeks. Generally, theamount of topical formulation administered is that which is sufficientto apply from about 0.1 to 100 μg/cm² of the VRP, based on the surfacearea of the wound.

The VRP can be used as a post-operative wound healing agent in balloonangioplasty, a procedure in which vascular endothelial cells are removedor damaged, together with compression of atherosclerotic plaques. TheVRP can be applied to inner vascular surfaces by systemic or localintravenous application either as intravenous bolus injection orinfusions. If desired, the VRP can be administered over time using amicrometering pump. Suitable compositions for intravenous administrationcomprise the VRP in an amount effective to promote endothelial cellgrowth and a parenteral carrier material. The VRP can be present in thecomposition over a wide range of concentrations, for example, from about50 μg/mL to about 1,000 μg/mL using injections of 3 to 10 mL perpatient, administered once or in dosing regimens that allow for multipleapplications. Any of the known parenteral carrier vehicles can be used,such as normal saline or 5-10% dextrose.

The VRP can also be used to promote endothelialization in vascular graftsurgery. In the case of vascular grafts using either transplantedvessels or synthetic material, for example, the VRP can be applied tothe surfaces of the graft and/or at the junctions of the graft and theexisting vasculature to promote the growth of vascular endothelialcells. For such applications, the VRP can be applied intravenously asdescribed above for balloon angioplasty or it can be applied directly tothe surfaces of the graft and/or the existing vasculature either beforeor during surgery. In such cases it may be desired to apply the VRP in athickened carrier material so that it will adhere to the affectedsurface. Suitable carrier materials include, for example, 1-5% carbopol.The VRP can be present in the carrier over a wide range ofconcentrations, for example, from about 50 μg/mg to about 1,000 μg/mg.Alternatively, the VRP can be delivered to the site by a micrometeringpump as a parenteral solution.

The VRP can also be employed to repair vascular damage followingmyocardial infarction and to circumvent the need for coronary bypasssurgery by stimulating the growth of a collateral circulation. The VRPis administered intravenously for this purpose, either in individualinjections or by micrometering pump over a period of time as describedabove or by direct infusion or injection to the site of damaged cardialmuscle.

Therapeutic formulations of VRP are prepared for storage by mixing VRPhaving the desired degree of purity with optional physiologicallyacceptable carriers, excipients, or stabilizers (Remington'sPharmaceutical Sciences, 16th edition, Osol, A., Ed., [1980]), in theform of lyophilized cake or aqueous solutions. Acceptable carriers,excipients, or stabilizers are nontoxic to recipients at the dosages andconcentrations employed, and include buffers such as phosphate, citrate,and other organic acids; antioxidants including ascorbic acid; lowmolecular weight (less than about 10 residues) polypeptides; proteins,such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymerssuch as polyvinylpyrrolidone; amino acids such as glycine, glutamine,asparagine, arginine, or lysine; monosaccharides, disaccharides, andother carbohydrates including glucose, mannose, or dextrins; chelatingagents such as EDTA; sugar alcohols such as mannitol or sorbitol;salt-forming counter-ions such as sodium; and/or non-ionic surfactantssuch as Tween, Pluronics or polyethylene glycol (PEG).

The VRP also may be entrapped in microcapsules prepared, for example, bycoacervation techniques or by interfacial polymerization (for example,hydroxymethylcellulose or gelatin-microcapsules andpoly-[methylmethacylate] microcapsules, respectively), in colloidal drugdelivery systems (for example, liposomes, albumin microspheres,microemulsions, nano-particles, and nanocapsules), or in macroemulsions.Such techniques are disclosed in Remington's Pharmaceutical Sciences,supra.

VRP to be used for in vivo administration must be sterile. This isreadily accomplished by filtration through sterile filtration membranes,prior to or following lyophilization and reconstitution. VRP ordinarilywill be stored in lyophilized form or in solution.

Therapeutic VRP compositions generally are placed into a containerhaving a sterile access port, for example, an intravenous solution bagor vial having a stopper pierceable by a hypodermic injection needle.

The route of VRP administration is in accord with known methods, e.g.,those routes set forth above for specific indications, as well as thegeneral routes of injection or infusion by intravenous, intraperitoneal,intracerebral, intramuscular, intraocular, intraarterial, orintralesional means, or sustained release systems as noted below. VRP isadministered continuously by infusion or by bolus injection. Generally,where the disorder permits, one should formulate and dose the VRP forsite-specific delivery. This is convenient in the case of wounds andulcers.

Suitable examples of sustained-release preparations includesemipermeable matrices of solid hydrophobic polymers containing theprotein, which matrices are in the form of shaped articles, e.g., films,or microcapsules. Examples of sustained-release matrices includepolyesters, hydrogels [e.g., poly(2-hydroxyethyl-methacrylate) asdescribed by Langer et al., J. Biomed. Mater. Res., 15:167-277 (1981)and Langer, Chem. Tech., 12:98-105 (1982) or poly(vinylalcohol)],polylactides (U.S. Pat. No. 3,773,919, EP 58,481), copolymers ofL-glutamnic acid and gamma ethyl-L-glutamate (Sidman et al.,Biopolymers, 22:547-556 [1983]), non-degradable ethylene-vinyl acetate(Langer et al., supra), degradable lactic acid-glycolic acid copolymerssuch as the Lupron Depot™ (injectable microspheres composed of lacticacid-glycolic acid copolymer and leuprolide acetate), andpoly-D-(−)-3-hydroxybutyric acid (EP 133,988).

While polymers such as ethylene-vinyl acetate and lactic acid-glycolicacid enable release of molecules for over 100 days, certain hydrogelsrelease proteins for shorter time periods. When encapsulated proteinsremain in the body for a long time, they may denature or aggregate as aresult of exposure to moisture at 37° C., resulting in a loss ofbiological activity and possible changes in immunogenicity. Rationalstrategies can be devised for protein stabilization depending on themechanism involved. For example, if the aggregation mechanism isdiscovered to be intermolecular S-S bond formation throughthio-disulfide interchange, stabilization may be achieved by modifyingsulfhydryl residues, lyophilizing from acidic solutions, controllingmoisture content, using appropriate additives, and developing specificpolymer matrix compositions.

Sustained-release VRP compositions also include liposomally entrappedVRP. Liposomes containing VRP are prepared by methods known per se: DE3,218,121; Epstein et al., Proc. Natl. Acad. Sci. USA 82:3688-3692(1985); Hwang et al., Proc. Natl. Acad. Sci. USA, 77:4030-4034 (1980);EP 52,322; EP 36,676; EP 88,046; EP 143,949; EP 142,641; Japanese patentapplication 83-118008; U.S. Pat. Nos. 4,485,045 and 4,544,545; and EP102,324. Ordinarily the liposomes are of the small (about 200-800Angstroms) unilamellar type in which the lipid content is greater thanabout 30 mol. % cholesterol, the selected proportion being adjusted forthe optimal VRP therapy.

When applied topically, the VRP is suitably combined with otheringredients, such as carriers and/or adjuvants. There are no limitationson the nature of such other ingredients, except that they must bepharmaceutically acceptable and efficacious for their intendedadministration, and cannot degrade the activity of the activeingredients of the composition. Examples of suitable vehicles includeointments, creams, gels, or suspensions, with or without purifiedcollagen. The compositions also may be impregnated into transdermalpatches, plasters, and bandages, preferably in liquid or semi-liquidform.

For obtaining a gel formulation, the VRP formulated in a liquidcomposition may be mixed with an effective amount of a water-solublepolysaccharide or synthetic polymer such as PEG to form a gel of theproper viscosity to be applied topically. The polysaccharide that may beused includes, for example, cellulose derivatives such as etherifiedcellulose derivatives, including alkyl celluloses, hydroxyalkylcelluloses, and alkylhydroxyalkyl celluloses, for example,methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose,hydroxypropyl methylcellulose, and hydroxypropyl cellulose; starch andfractionated starch; agar; alginic acid and alginates; gum arabic;pullullan; agarose; carrageenan; dextrans; dextrins; fructans; inulin;mannans; xylans; arabinans; chitosans; glycogens; glucans; and syntheticbiopolymers; as well as gums such as xanthan gum; guar gum; locust beangum; gum arabic; tragacanth gum; and karaya gum; and derivatives andmixtures thereof. The preferred gelling agent herein is one that isinert to biological systems, nontoxic, simple to prepare, and not toorunny or viscous, and will not destabilize the VRP held within it.

Preferably the polysaccharide is an etherified cellulose derivative,more preferably one that is well defined, purified, and listed in USP,e.g., methylcellulose and the hydroxyalkyl cellulose derivatives, suchas hydroxypropyl cellulose, hydroxyethyl cellulose, and hydroxypropylmethylcellulose. Most preferred herein is methylcellulose.

The polyethylene glycol useful for gelling is typically a mixture of lowand high molecular weight PEGs to obtain the proper viscosity. Forexample, a mixture of a PEG of molecular weight 400-600 with one ofmolecular weight 1500 would be effective for this purpose when mixed inthe proper ratio to obtain a paste.

The term “water soluble” as applied to the polysaccharides and PEGs ismeant to include colloidal solutions and dispersions. In general, thesolubility of the cellulose derivatives is determined by the degree ofsubstitution of ether groups, and the stabilizing derivatives usefulherein should have a sufficient quantity of such ether groups peranhydroglucose unit in the cellulose chain to render the derivativeswater soluble. A degree of ether substitution of at least 0.35 ethergroups per anhydroglucose unit is generally sufficient. Additionally,the cellulose derivatives may be in the form of alkali metal salts, forexample, the Li, Na, K, or Cs salts.

If methylcellulose is employed in the gel, preferably it comprises about2-5%, more preferably about 3%, of the gel and the VRP is present in anamount of about 300-1000 mg per ml of gel.

An effective amount of VRP to be employed therapeutically will depend,for example, upon the therapeutic objectives, the route ofadministration, and the condition of the patient. Accordingly, it willbe necessary for the therapist to titer the dosage and modify the routeof administration as required to obtain the optimal therapeutic effect.Typically, the clinician will administer the VRP until a dosage isreached that achieves the desired effect. A typical daily dosage forsystemic treatment might range from about 1 μg/kg to up to 10 mg/kg ormore, depending on the factors mentioned above. As an alternativegeneral proposition, the VRP is formulated and delivered to the targetsite or tissue at a dosage capable of establishing in the tissue a VRPlevel greater than about 0.1 ng/cc up to a maximum dose that isefficacious but not unduly toxic. This intra-tissue concentration shouldbe maintained if possible by continuous infusion, sustained release,topical application, or injection at empirically determined frequencies.The progress of this therapy is easily monitored by conventional assays.

It is within the scope hereof to combine the VRP therapy with othernovel or conventional therapies (e.g., growth factors such as VEGF,acidic or basic fibroblast growth factor (aFGF or bFGF, respectively),platelet-derived growth factor (PDGF), insulin-like growth factor (IGF-Ior IGF-II), nerve growth factor (NGF), anabolic steroids, EGF or TGF-α)for enhancing the activity of any of the growth factors, including theVRP, in promoting cell proliferation and repair. It is not necessarythat such co-treatment drugs be included per se in the compositions ofthis invention, although this will be convenient where such drugs areproteinaceous. Such admixtures are suitably administered in the samemanner and for the same purposes as the VRP used alone. The useful molarratio of VRP to such secondary growth factors is typically 1:0.1-10,with about equimolar amounts being preferred.

3. Non-Therapeutic, Diagnostic Uses for VRP

The nucleic acid encoding the VRP may be used as a diagnostic fortissue-specific typing. For example, such procedures as in situhybridization, Northern and Southern blotting, and PCR analysis may beused to determine whether DNA and/or RNA encoding VRP is present in thecell type(s) being evaluated. VRP nucleic acid or polypeptide may alsobe used as diagnostic markers. For example, the VRP may be labeled,using the techniques described herein, and expression of nucleic acidmolecules encoding a Flt4 receptor or another VRP receptor can bequantified, using the labelled VRP.

If the human VRP-encoding nucleic acid is localized to a humanchromosome, the nucleic acid for human VRP can be used as a marker forthis human chromosome.

VRP nucleic acid is also useful for the preparation of VRP polypeptideby recombinant techniques exemplified herein.

Isolated VRP polypeptide may be used in quantitative diagnostic assaysas a standard or control against which samples containing unknownquantities of VRP may be prepared.

VRP preparations are also useful in generating antibodies, as standardsin assays for VRP (e.g., by labeling VRP for use as a standard in aradioimmunoassay, radioreceptor assay, or enzyme-linked immunoassay),for detecting the presence of the Flt4 receptor or one or more other VRPreceptors in a biological sample (e.g., using a labeled VRP), inaffinity purification techniques, and in competitive-type receptorbinding assays when labeled with radioiodine, enzymes, fluorophores,spin labels, or the like.

The VRP is also useful as a diagnostic tool. For example, the VRP can beproduced in prokaryotic cells using the techniques elaborated herein andthe unglycosylated protein so produced can be used as a molecular weightmarker. The deduced molecular weight (mw) of the VRP is about 44.8 kDa.To use the VRP as a molecular weight marker, gel filtrationchromatography or SDS-PAGE, for example, will be used to separateprotein(s) for which it is desired to determine their molecularweight(s) in substantially the normal way. The VRP and other molecularweight markers will be used as standards to provide a range of molecularweights. For example, phosphorylase b (mw=97,400), bovine serum albumin(mw=68,000), ovalbumin (mw=46,000), VRP (mw=44,800), trypsin inhibitor(mw=20,100), and lysozyme (mw=14,400) can be used a mw markers. Theother molecular weight markers mentioned here can be purchasedcommercially from Amersham Corporation, Arlington Heights, Ill., forexample. Often, the molecular weight markers will be labeled to enableeasy detection following separation. Techniques for labeling antibodiesand proteins are discussed herein and are well known in the art. Forexample, the molecular weight markers may be biotinylated and, followingseparation on SDS-PAGE, for example, the blot can be incubated withstreptavidin-horseradish peroxidase. The bands can then be detected bylight detection.

It may also be useful to grow certain cells having the Flt4 receptor orone or more other VRP receptors ex vivo using the VRP as an angiogenicfactor or growth factor. Thus, for example, the VRP can be used as agrowth factor in the in vitro culturing of endothelial cells. For suchuses, the VRP can be added to the cell culture medium at a concentrationfrom about 10 pg/mL to about 10 ng/mL.

These cells which are to be grown ex vivo may simultaneously be exposedto other known growth factors or cytokines. Exemplary cytokines includethe interleukins (e.g., IL-3), granulocyte-macrophage colony-stimulatingfactor (GM-CSF), VEGF, macrophage colony-stimulating factor (M-CSF),granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophagecolony-stimulating factor (GM-CSF), erythropoietin (Epo), lymphotoxin,steel factor (SLF), tumor necrosis factor (TNF), and gamma-interferon.This results in proliferation and/or differentiation of the cells havingthe Flt4 receptor or one or more other VRP receptors.

In yet another aspect of the invention, the VRP may be used for affinitypurification of the Flt4 receptor or one or more other VRP receptors.Briefly, this technique involves covalently attaching the VRP to aninert and porous matrix (e.g., agarose reacted with cyanogen bromide). Asolution containing the Flt4 receptor or other VRP receptor(s) can thenbe passed through the chromatographic material and can be subsequentlyreleased by changing the elution conditions (e.g. by changing pH orionic strength).

The purified VRP, and the nucleic acid encoding it, may also be sold asreagents for mechanism studies of VRP and its cognate receptors, tostudy the role of the VRP and the Flt4 receptor or other VRP receptorsin normal growth and development, as well as abnormal growth anddevelopment, e.g. in malignancies.

The VRP may be used for competitive screening of potential agonists orantagonists for binding to the Flt4 receptor or other VRP receptors. VRPvariants are useful as standards or controls in assays for the VRP,provided that they are recognized by the analytical system employed,e.g. an anti-VRP antibody.

4. VRP Antibody Preparation

A description follows as to the production of exemplary antibodies asdefined herein. These exemplary antibodies include polyclonal,monoclonal, humanized, bispecific, or heteroconjugate antibodies.

A. Polyclonal Antibodies

Polyclonal antibodies to the VRP generally are raised in animals bymultiple subcutaneous (sc) or intraperitoneal (ip) injections of the VRPand an adjuvant. It may be useful to conjugate the VRP to a protein thatis immunogenic in the species to be immunized, e.g., keyhole limpethemocyanin, serum albumin, bovine thyroglobulin, or soybean trypsininhibitor using a bifunctional or derivatizing agent, for examplemaleimidobenzoyl sulfosuccinimide ester (conjugation through cysteineresidues), N-hydroxysuccinimide (through lysine residues),glytaraldehyde, succinic anhydride, SOCl₂, or R¹N═C═NR, where R and R¹are different alkyl groups.

Animals are immunized against the immunogenic conjugates or derivativesby combining 1 mg of 1 μg of conjugate (for rabbits or mice,respectively) with 3 volumes of 5 Freud's complete adjuvant andinjecting the solution intradermally at multiple sites. One month laterthe animals are boosted with ⅕ to 1/10 the original amount of conjugatein Freud's complete adjuvant by subcutaneous injection at multiplesites. Seven to 14 days later the animals are bled and the serum isassayed for anti-VRP antibody titer. Animals are boosted until the titerplateaus. Preferably, the animal is boosted with a conjugate of the sameVRP with a different protein and/or the conjugation is through adifferent cross-linking reagent. Conjugates also can be made inrecombinant cell culture as protein fusions. Also, aggregating agentssuch as alum are used to enhance the immune response.

B. Monoclonal Antibodies

Monoclonal antibodies are obtained from a population of substantiallyhomogeneous antibodies, i.e., the individual antibodies comprising thepopulation are identical except for possible naturally-occurringmutations that may be present in minor amounts. Thus, the modifier“monoclonal” indicates the character of the antibody as not being amixture of discrete antibodies.

For example, the anti-VRP monoclonal antibodies of the invention may bemade using the hybridoma method first described by Kohler and Milstein,Nature, 256:495 (1975), or may be made by recombinant DNA methods. U.S.Pat. No. 4,816,567.

In the hybridoma method, a mouse or other appropriate host animal, suchas hamster, is immunized as hereinabove described to elicit lymphocytesthat produce, or are capable of producing, antibodies that willspecifically bind to the protein used for immunization. Alternatively,lymphocytes may be immunized in vitro. Lymphocytes then are fused withmyeloma cells using a suitable fusing agent, such as PEG, to form ahybridoma cell. Goding, Monoclonal Antibodies: Principles and Practice,pp. 59-103 (Academic Press, 1986).

The hybridoma cells thus prepared are seeded and grown in a suitableculture medium that preferably contains one or more substances thatinhibit the growth or survival of the unfused, parental myeloma cells.For example, if the parental myeloma cells lack the enzyme hypoxanthineguanine phosphoribosyl transferase (HGPRT or HPRT), the culture mediumfor the hybridomas typically will include hypoxanthine, aminopterin, andthymidine (HAT medium), which substances prevent the growth ofHGPRT-deficient cells.

Preferred myeloma cells are those that fuse efficiently, support stablehigh-level expression of antibody by the selected antibody-producingcells, and are sensitive to a medium such as HAT medium. Among these,preferred myeloma cell lines are murine myeloma lines, such as thosederived from MOPC-21 and MPC-11 mouse tumors available from the SalkInstitute Cell Distribution Center, San Diego, Calif., USA, and SP-2cells available from the American Type Culture Collection, Rockville,Md. USA. Human myeloma and mouse-human heteromyeloma cell lines alsohave been described for the production of human monoclonal antibodies.Kozbor, J. Immunol., 133:3001 (1984); Brodeur et al., MonoclonalAntibody Production Techniques and Applications, pp. 51-63 (MarcelDekker, Inc., New York, 1987). See, also, Boerner et al., J. Immunol.,147:86-95 (1991) and WO 91/17769, published 28 Nov. 1991, for techniquesfor the production of human monoclonal antibodies.

Culture medium in which hybridoma cells are growing is assayed forproduction of monoclonal antibodies directed against VRP. Preferably,the binding specificity of monoclonal antibodies produced by hybridomacells is determined by immunoprecipitation or by an in vitro bindingassay, such as radioimmunoassay (RIA) or enzyme-linked immunoabsorbentassay (ELISA).

The binding affinity of the monoclonal antibody can, for example, bedetermined by the Scatchard analysis of Munson and Pollard, Anal.Biochem., 107:220 (1980).

After hybridoma cells are identified that produce antibodies of thedesired specificity, affinity, and/or activity, the clones may besubcloned by limiting dilution procedures and grown by standard methods.Goding, Monoclonal Antibodies: Principles and Practice, pp. 59-104(Academic Press, 1986). Suitable culture media for this purpose include,for example, Dulbecco's Modified Eagle's Medium or RPMI-1640 medium. Inaddition, the hybridoma cells may be grown in vivo as ascites tumors inan animal.

The monoclonal antibodies secreted by the subclones are suitablyseparated from the culture medium, ascites fluid, or serum byconventional immunoglobulin purification procedures such as, forexample, protein A-Sepharose, hydroxylapatite chromatography, gelelectrophoresis, dialysis, or affinity chromatography.

Alternatively, it is now possible to produce transgenic animals (e.g.mice) that are capable, upon immunization, of producing a fullrepertoire of human antibodies in the absence of endogenousimmunoglobulin production. For example, it has been described that thehomozygous deletion of the antibody heavy chain joining region (J_(H))gene in chimeric and germ-line mutant mice results in completeinhibition of endogenous antibody production. Transfer of the humangerm-line immunoglobulin gene array in such germ-line mutant mice willresult in the production of human antibodies upon antigen challenge.See, e.g. Jakobovits et al., Proc. Natl. Acad. Sci. USA, 90:2551-255(1993); Jakobovits et al., Nature, 362:255-258 (1993).

In a further embodiment, antibodies or antibody fragments can beisolated from antibody phage libraries generated using the techniquesdescribed in McCafferty et al., Nature, 348:552-554 (1990), using theVRP to select for a suitable antibody or antibody fragment. Clackson etal., Nature, 352:624-628 (1991) and Marks et al., J. Mol. Biol.,222:581-597 (1991) describe the isolation of murine and humanantibodies, respectively, using phage libraries. Subsequent publicationsdescribe the production of high-affinity (nM range) human antibodies bychain shuffling (Mark et al., Bio/Technol., 10:779-783 [1992]), as wellas combinatorial infection and in vivo recombination as a strategy forconstructing very large phage libraries. Waterhouse et al., Nuc. AcidsRes., 21:2265-2266 (1993). Thus, these techniques are viablealternatives to traditional monoclonal antibody hybridoma techniques forisolation of “monoclonal” antibodies (especially human antibodies) thatare encompassed by the present invention.

DNA encoding the monoclonal antibodies of the invention is readilyisolated and sequenced using conventional procedures (e.g., by usingoligonucleotide probes that are capable of binding specifically to genesencoding the heavy and light chains of murine antibodies). The hybridomacells of the invention serve as a preferred source of such DNA. Onceisolated, the DNA may be placed into expression vectors, which are thentransfected into host cells such as simian COS cells, Chinese hamsterovary (CHO) cells, or myeloma cells that do not otherwise produceimmunoglobulin protein, to obtain the synthesis of monoclonal antibodiesin the recombinant host cells. The DNA also may be modified, forexample, by substituting the coding sequence for human heavy- andlight-chain constant domains in place of the homologous murine sequences(Morrison et al., Proc. Nat. Acad. Sci. USA, 81, 6851 [1984]), or bycovalently joining to the immunoglobulin coding sequence all or part ofthe coding sequence for a non-inmuunoglobulin polypeptide. In thatmanner, “chimeric” or “hybrid” antibodies are prepared that have thebinding specificity of an anti-VRP monoclonal antibody herein.

Typically, such non-immunoglobulin polypeptides are substituted for theconstant domains of an antibody of the invention, or they aresubstituted for the variable domains of one antigen-combining site of anantibody of the invention to create a chimeric bivalent antibodycomprising one antigen-combining site having specificity for an VRP andanother antigen-combining site having specificity for a differentantigen.

Chimeric or hybrid antibodies also may be prepared in vitro using knownmethods in synthetic protein chemistry, including those involvingcrosslinking agents. For example, immunotoxins may be constructed usinga disulfide exchange reaction or by forming a thioether bond. Examplesof suitable reagents for this purpose include iminothiolate andmethyl-4-mercaptobutyrimidate.

For diagnostic applications, the antibodies of the invention typicallywill be labeled with a detectable moiety. The detectable moiety can beany one which is capable of producing, either directly or indirectly, adetectable signal. For example, the detectable moiety may be aradioisotope, such as ³H, ¹⁴C, ³²P, ³⁵S, or ¹²⁵I; a fluorescent orchemiluminescent compound, such as fluorescein isothiocyanate,rhodamine, or luciferin; or an enzyme, such as alkaline phosphatase,beta-galactosidase, or horseradish peroxidase.

Any method known in the art for separately conjugating the antibody tothe detectable moiety may be employed, including those methods describedby Hunter et al., Nature, 144:945 (1962); David et al., Biochemistry,13:1014 (1974); Pain et al., J. Immunol. Meth., 40:219 (1981); andNygren, J. Histochem. and Cytochem., 30:407 (1982).

The antibodies of the present invention may be employed in any knownassay method, such as competitive binding assays, direct and indirectsandwich assays, and immunoprecipitation assays. Zola, MonoclonalAntibodies: A Manual of Techniques, pp. 147-158 (CRC Press, Inc., 1987).

Competitive binding assays rely on the ability of a labeled standard(which may be a VRP, or an immunologically reactive portion thereof) tocompete with the test sample analyte (VRP) for binding with a limitedamount of antibody. The amount of VRP in the test sample is inverselyproportional to the amount of standard that becomes bound to theantibodies. To facilitate determining the amount of standard thatbecomes bound, the antibodies generally are insolubilized before orafter the competition, so that the standard and analyte that are boundto the antibodies may conveniently be separated from the standard andanalyte which remain unbound.

Sandwich assays involve the use of two antibodies, each capable ofbinding to a different immunogenic portion, or epitope, of the proteinto be detected (VRP). In a sandwich assay, the test sample analyte isbound by a first antibody which is immobilized on a solid support, andthereafter a second antibody binds to the analyte, thus forming aninsoluble three-part complex. See, e.g., U.S. Pat. No. 4,376,110. Thesecond antibody may itself be labeled with a detectable moiety (directsandwich assays) or may be measured using an anti-immunoglobulinantibody that is labeled with a detectable moiety (indirect sandwichassay). For example, one type of sandwich assay is an ELISA assay, inwhich case the detectable moiety is an enzyme.

C. Humanized Antibodies

Methods for humanizing non-human antibodies are well known in the art.Generally, a humanized antibody has one or more amino acid residuesintroduced into it from a source which is non-human. These non-humanamino acid residues are often referred to as “import” residues, whichare typically taken from an “import” variable domain. Humanization canbe essentially performed following the method of Winter and co-workers(Jones et al., Nature, 321:522-525 [1986]; Riechmann et al., Nature332:323-327 [1988]; Verhoeyen et al., Science, 239:1534-1536 [1988]), bysubstituting rodent CDRs or CDR sequences for the correspondingsequences of a human antibody. Accordingly, such “humanized” antibodiesare chimeric antibodies (U.S. Pat. No. 4,816,567, supra), whereinsubstantially less than an intact human variable domain has beensubstituted by the corresponding sequence from a non-human species. Inpractice, humanized antibodies are typically human antibodies in whichsome CDR residues, and possibly some FR residues, are substituted byresidues from analogous sites in rodent antibodies.

It is important that antibodies be humanized with retention of highaffinity for the antigen and other favorable biological properties. Toachieve this goal, according to a preferred method, humanized antibodiesare prepared by a process of analysis of the parental sequences andvarious conceptual humanized products using three-dimensional models ofthe parental and humanized sequences. Three-dimensional immunoglobulinmodels are familiar to those skilled in the art. Computer programs areavailable which illustrate and display probable three-dimensionalconformational structures of selected candidate immunoglobulinsequences. Inspection of these displays permits analysis of the likelyrole of the residues in the functioning of the candidate immunoglobulinsequence, i.e., the analysis of residues that influence the ability ofthe candidate immunoglobulin to bind its antigen. In this way, FRresidues can be selected and combined from the consensus and importsequence so that the desired antibody characteristic, such as increasedaffinity for the target antigen(s), is achieved. In general, the CDRresidues are directly and most substantially involved in influencingantigen binding. For further details see WO 92/22653, published 23 Dec.1992.

D. Bispecific Antibodies

Bispecific antibodies are monoclonal, preferably human or humanized,antibodies that have binding specificities for at least two differentantigens. In the present case, one of the binding specificities is forthe VRP, the other one is for any other antigen, and preferably for areceptor or receptor subunit. For example, bispecific antibodiesspecifically binding the Flt4 receptor and the VRP are within the scopeof the present invention.

Methods for making bispecific antibodies are known in the art.Traditionally, the recombinant production of bispecific antibodies isbased on the co-expression of two immunoglobulin heavy-chain/light-chainpairs, where the two heavy chains have different specificities.Millstein and Cuello, Nature, 305:537-539 (1983). Because of the randomassortment of immunoglobulin heavy and light chains, these hybridomas(quadromas) produce a potential mixture of ten different antibodymolecules, of which only one has the correct bispecific structure. Thepurification of the correct molecule, which is usually done by affinitychromatography steps, is rather cumbersome, and the product yields arelow. Similar procedures are disclosed in WO 93/08829, published 13 May1993, and in Traunecker et al., EMBO J., 10:3655-3659 (1991).

According to a different and more preferred approach, antibody variabledomains with the desired binding specificities (antibody-antigencombining sites) are fused to immunoglobulin constant domain sequences.The fusion preferably is with an immunoglobulin heavy-chain constantdomain, comprising at least part of the hinge, CH2, and CH3 regions. Itis preferred to have the first heavy-chain constant region (CH1)containing the site necessary for light-chain binding present in atleast one of the fusions. DNAs encoding the immunoglobulin heavy-chainfusions and, if desired, the immunoglobulin light chain, are insertedinto separate expression vectors, and are co-transfected into a suitablehost organism. This provides for great flexibility in adjusting themutual proportions of the three polypeptide fragments in embodimentswhen unequal ratios of the three polypeptide chains used in theconstruction provide the optimum yields. It is, however, possible toinsert the coding sequences for two or all three polypeptide chains inone expression vector when the expression of at least two polypeptidechains in equal ratios results in high yields or when the ratios are ofno particular significance. In a preferred embodiment of this approach,the bispecific antibodies are composed of a hybrid immunoglobulin heavychain with a first binding specificity in one arm, and a hybridimmunoglobulin heavy-chain/light-chain pair (providing a second bindingspecificity) in the other arm. It was found that this asymmetricstructure facilitates the separation of the desired bispecific compoundfrom unwanted immunoglobulin chain combinations, as the presence of animmunoglobulin light chain in only one half of the bispecific moleculeprovides for a facile way of separation. This approach is disclosed inWO 94/04690 published 3 Mar. 1994. For further details of generatingbispecific antibodies see, for example, Suresh et al., Methods inEnzymology, 121:210 (1986).

E. Heteroconjugate Antibodies

Heteroconjugate antibodies are also within the scope of the presentinvention. Heteroconjugate antibodies are composed of two covalentlyjoined antibodies. Such antibodies have, for example, been proposed totarget immune system cells to unwanted cells (U.S. Pat. No. 4,676,980),and for treatment of HIV infection. WO 91/00360; WO 92/200373; EP 03089.Heteroconjugate antibodies may be made using any convenientcross-linking methods. Suitable cross-linking agents are well known inthe art, and are disclosed, for example, in U.S. Pat. No. 4,676,980,along with a number of cross-linking techniques.

5. Uses of VRP Antibodies

i. Therapeutic Uses

VRP antibodies may be useful in certain therapeutic indications to blockactivity of the VRP (for example, to block excess activation orinhibition of the Flt4 receptor or another receptor that binds to VRP,and to block neovascularization, re-endothelialization, andangiogenesis). Specifically, the VRP antibodies are useful in thetreatment of various neoplastic and non-neoplastic diseases anddisorders. Neoplasms and related conditions that are amenable totreatment include breast carcinomas, lung carcinomas, gastriccarcinomas, esophageal carcinomas, colorectal carcinomas, livercarcinomas, ovarian carcinomas, thecomas, arrhenoblastomas, cervicalcarcinomas, endometrial carcinoma, endometrial hyperplasia,endometriosis, fibrosarcomas, choriocarcinoma, head and neck cancer,nasopharyngeal carcinoma, laryngeal carcinomas, hepatoblastoma, Kaposi'ssarcoma, melanoma, skin carcinomas, hemangioma, cavernous hemangioma,hemangioblastoma, pancreas carcinomas, retinoblastoma, astrocytoma,glioblastoma, Schwannoma, oligodendroglioma, medulloblastoma,neuroblastomas, rhabdomyosarcoma, osteogenic sarcoma, leiomyosarcomas,urinary tract carcinomas, thyroid carcinomas, Wilm's tumor, renal cellcarcinoma, prostate carcinoma, abnormal vascular proliferationassociated with phakomatoses, edema (such as that associated with braintumors), and Meigs' syndrome.

Non-neoplastic conditions that are amenable to treatment includerheumatoid arthritis, psoriasis, atherosclerosis, diabetic and otherretinopathies, retrolental fibroplasia, neovascular glaucoma,age-related macular degeneration, thyroid hyperplasias (includingGrave's disease), corneal and other tissue transplantation, chronicinflammation, lung inflammation, nephrotic syndrome, preeclampsia,ascites, pericardial effusion (such as that associated withpericarditis), and pleural effusion.

Age-related macular degeneration (AMD) is a leading cause of severevisual loss in the elderly population. The exudative form of AMD ischaracterized by choroidal neovascularization and retinal pigmentepithelial cell detachment. Because choroidal neovascularization isassociated with a dramatic worsening in prognosis, the VRP antibodies ofthe present invention are expected to be especially useful in reducingthe severity of AMD.

For therapeutic applications, the VRP antibodies of the invention areadministered to a mammal, preferably a human, in a pharmaceuticallyacceptable dosage form, including those that may be administered to ahuman intravenously as a bolus or by continuous infusion over a periodof time, by intramuscular, intraperitoneal, intra-cerobrospinal,subcutaneous, intra-articular, intrasynovial, intrathecal, oral,topical, or inhalation routes. The VRP antibodies also are suitablyadministered by intratumoral, peritumoral, intralesional, orperilesional routes or to the lymph, to exert local as well as systemictherapeutic effects. The intraperitoneal route is expected to beparticularly useful, for example, in the treatment of ovarian tumors.

Such dosage forms encompass pharmaceutically acceptable carriers thatare inherently non-toxic and non-therapeutic. Examples of such carriersinclude ion exchangers, alumina, aluminum stearate, lecithin, serumproteins, such as human serum albumin, buffer substances such asphosphates, glycine, sorbic acid, potassium sorbate, partial glyceridemixtures of saturated vegetable fatty acids, water, salts, orelectrolytes such as protamine sulfate, disodium hydrogen phosphate,potassium hydrogen phosphate, sodium chloride, zinc salts, colloidalsilica, magnesium trisilicate, polyvinyl pyrrolidone, cellulose-basedsubstances, and PEG. Carriers for topical or gel-based forms of VRPantibodies include polysaccharides such as sodium carboxymethylcelluloseor methylcellulose, polyvinylpyrrolidone, polyacrylates,polyoxyethylene-polyoxypropylene-block polymers, PEG, and wood waxalcohols. For all administrations, conventional depot forms are suitablyused. Such forms include, for example, microcapsules, nano-capsules,liposomes, plasters, inhalation forms, nose sprays, sublingual tablets,and sustained-release preparations. The VRP antibody will typically beformulated in such vehicles at a concentration of about 0.1 mg/ml to 100mg/ml.

Suitable examples of sustained-release preparations includesemipermeable matrices of solid hydrophobic polymers containing the VRPantibody, which matrices are in the form of shaped articles, e.g. films,or microcapsules. Examples of sustained-release matrices includepolyesters, hydrogels (for example, poly(2-hydroxyethyl-methacrylate) asdescribed by Langer et al., supra and Langer, supra, orpoly(vinylalcohol), polylactides (U.S. Pat. No. 3,773,919), copolymersof L-glutamic acid and gamma ethyl-L-glutamate (Sidman et al., supra),non-degradable ethylene-vinyl acetate (Langer et al., supra), degradablelactic acid-glycolic acid copolymers such as the Lupron Depot™(injectable micropheres composed of lactic acid-glycolic acid copolymerand leuprolide acetate), and poly-D-(-)-3-hydroxybutyric acid. Whilepolymers such as ethylene-vinyl acetate and lactic acid-glycolic acidenable release of molecules for over 100 days, certain hydrogels releaseproteins for shorter time periods. When encapsulated VRP antibodiesremain in the body for a long time, they may denature or aggregate as aresult of exposure to moisture at 37° C., resulting in a loss ofbiological activity and possible changes in immunogenicity. Rationalstrategies can be devised for stabilization depending on the mechanisminvolved. For example, if the aggregation mechanism is discovered to beintermolecular S—S bond formation through thio-disulfide interchange,stabilization may be achieved by modifying sulfhydryl residues,lyophilizing from acidic solutions, controlling moisture content, usingappropriate additives, and developing specific polymer matrixcompositions.

Sustained-release VRP antibody compositions also include liposomallyentrapped antibodies. Liposomes containing the VRP antibodies areprepared by methods known in the art, such as described in Epstein etal., Proc. Natl. Acad. Sci. USA, 82:3688 (1985); Hwang et al., Proc.Natl. Acad. Sci. USA, 77:4030 (1980); and U.S. Pat. Nos. 4,485,045 and4,544,545. Ordinarily, the liposomes are the small (about 200-800Angstroms) unilamelar type in which the lipid content is greater thanabout 30 mol. % cholesterol, the selected proportion being adjusted forthe optimal VRP antibody therapy. Liposomes with enhanced circulationtime are disclosed in U.S. Pat. No. 5,013,556.

Another use of the present invention comprises incorporating VRPantibodies into formed articles. Such articles can be used in modulatingendothelial cell growth and angiogenesis. In addition, tumor invasionand metastasis may be modulated with these articles.

For the prevention or treatment of disease, the appropriate dosage ofVRP antibody will depend on the type of disease to be treated, asdefined above, the severity and course of the disease, whether theantibodies are administered for preventive or therapeutic purposes,previous therapy, the patient's clinical history and response to the VRPantibody, and the discretion of the attending physician. The VRPantibody is suitably administered to the patient at one time or over aseries of treatments.

Depending on the type and severity of the disease, about 1 μg/kg to 15mg/kg of VRP antibody is an initial candidate dosage for administrationto the patient, whether, for example, by one or more separateadministrations, or by continuous infusion. A typical daily dosage mightrange from about 1 μg/kg to 100 mg/kg or more, depending on the factorsmentioned above. For repeated administrations over several days orlonger, depending on the condition, the treatment is sustained until adesired suppression of disease symptoms occurs. However, other dosageregimens may be useful. The progress of this therapy is easily monitoredby conventional techniques and assays, including, for example,radiographic tumor imaging.

According to another embodiment of the invention, the effectiveness ofthe VRP antibody in preventing or treating disease may be improved byadministering the VRP antibody serially or in combination with anotherproteinaceous agent that is effective for those purposes, such as thoseenumerated below, or one or more conventional therapeutic agents suchas, for example, alkylating agents, folic acid antagonists,anti-metabolites of nucleic acid metabolism, antibiotics, pyrimidineanalogs, 5-fluorouracil, cisplatin, purine nucleosides, amines, aminoacids, triazol nucleosides, or corticosteroids. Such other agents may bepresent in the composition being administered or may be administeredseparately. Also, the VRP antibody is suitably administered serially orin combination with radiological treatments, whether involvingirradiation or administration of radioactive substances.

In one embodiment, vascularization of tumors is attacked in combinationtherapy. One or more VRP antibodies are administered to tumor-bearingpatients at therapeutically effective doses as determined, for example,by observing necrosis of the tumor or its metastatic foci, if any. Thistherapy is continued until such time as no further beneficial effect isobserved or clinical examination shows no trace of the tumor or anymetastatic foci. Then the proteinaceous auxiliary agent is administered,alone or in combination with another auxiliary agent. Such agentsinclude, e.g., TNF, an antibody capable of inhibiting or neutralizingthe angiogenic activity of aFGF or bFGF or hepatocyte growth factor(HGF), an rhVEGF antagonist as described in WO 94/10202, supra, alpha-,beta-, or gamma-interferon, anti-HER2 antibody, heregulin,anti-heregulin antibody, D-factor, interleukin-1 (IL-1), interleukin-2(IL-2), GM-CSF, or agents that promote microvascular coagulation intumors, such as anti-protein C antibody, anti-protein S antibody, or C4bbinding protein (WO 91/01753 published 21 Feb. 1991), or heat orradiation.

Since the auxiliary agents will vary in their effectiveness it isdesirable to compare their impact on the tumor by matrix screening inconventional fashion. The administration of VRP antibody and TNF and/orother auxiliary agent is repeated until the desired clinical effect isachieved. Alternatively, the VRP antibody or antibodies are administeredtogether with TNF and, optionally, other auxiliary agent(s). Ininstances where solid tumors are found in the limbs or in otherlocations susceptible to isolation from the general circulation, thetherapeutic agents described herein are administered to the isolatedtumor or organ. In other embodiments, a FGF or platelet-derived growthfactor (PDGF) antagonist, such as an anti-FGF or an anti-PDGFneutralizing antibody, is administered to the patient in conjunctionwith the VRP antibody. Treatment with VRP antibodies optimally may besuspended during periods of wound healing or desirableneovascularization.

ii. Other Uses

The VRP antibodies of the invention also are useful as affinitypurification agents. In this process, the antibodies against VRP areimmobilized on a suitable support, such a Sephadex resin or filterpaper, using methods well known in the art. The immobilized antibodythen is contacted with a sample containing the VRP to be purified, andthereafter the support is washed with a suitable solvent that willremove substantially all the material in the sample except the VRP,which is bound to the immobilized antibody. Finally, the support iswashed with another suitable solvent, such as glycine buffer, pH 5.0,that will release the VRP from the antibody.

VRP antibodies may also be useful in diagnostic assays for VRP, e.g.,detecting its expression in specific cells, tissues, or serum. Theantibodies are labeled in the same fashion as VRP described above and/orare immobilized on an insoluble matrix. VRP antibodies also are usefulfor the affinity purification of VRP from recombinant cell culture ornatural sources. VRP antibodies that do not detectably cross-react withother proteins can be used to purify VRP free from these other knownproteins. Suitable diagnostic assays for VRP and its antibodies aredescribed above.

III. Experimental

Below are examples of specific embodiments for carrying out the presentinvention. The examples are offered for illustrative purposes only, andare not intended to limit the scope of the present invention in any way.

All publications, patents and patent applications cited herein, whethersupra or infra, are hereby incorporated by reference in their entirety.

EXAMPLE 1 Isolation of cDNA Clones Encoding Human Flt4 Receptor

cDNA synthesized from mRNA purified from the human megakaryocyteleukemia cell line CMK11-5 was amplified with redundant PCR primersbased on the conserved regions of tyrosine kinase receptors. Wilks,Proc. Natl. Acad. Sci. USA, 86: 1603-1607 (1989). One amplified fragmentof about 180 bp with a unique DNA sequence (designated SAL-S1 or tk1;PCT/US93/00586, supra) was used to screen (Janssen et al, supra) cDNAlibraries from CMK11-5 and DAMI cells to obtain overlapping clones thatencoded the full-length short form of Flt4 receptor (1298 amino acids).The sequence of the assembled Flt4-encoding clones matched that reportedfrom an anerythroleukemia cell line (Pajusola et al., Cancer Res.,supra); it encodes 8 amino acid differences from another reported Flt4sequence. Galland et al., Oncogene, supra. Clones encoding the long formof Flt4 (1363 amino acids) were constructed by synthesizing thediffering 3′ DNA sequence of about 200 bp based on the publishedsequence. Pajusola et al., Oncogene, 8, supra.

EXAMPLE 2 Receptor IgG Fusion Proteins, Flt4/IgG Antiserum, and G61 FACSAnalysis

Flt1/IgG (Park et al., supra), Flk1/IgG (Park et al., supra), Rse/IgG(Godowski et al., Cell, 82: 355-358 [1995]), and Htk/IgG (Bennett etal., J. Biol. Chem., 269: 14211-14218 [1994]) were produced as describedin these references. For Flt4/IgG, DNA encoding the extracellular domainof the Flt4 receptor (amino acids 1-775) was spliced to the Fc region ofa human IgG heavy chain at the unique BstEII site in the plasmidpBSSK-Fc (pBSSK-CH2CH3). Bennett et al., J. Biol. Chem., 266:23060-23067 (1991). The open reading frame encoding Flt4/IgG was clonedin the mammalian expression vector pRK5 (Suva et al., Science, 237:893-896 [1987]) to yield the plasmid pRK5.tk1ig1.1. This plasmid wastransfected by electroporation (Janssen et al., supra) into 293 cells(ATCC CRL 1651), and after 3-4 days, Flt4/IgG was purified from theserum-free conditioned medium with protein A agarose (Calbiochem). Flt4antiserum was generated by injection of purified Flt4/IgG into rabbits.

By using this fusion protein to screen cell lines for membrane-bound VRPby FACS analysis, one positive cell line was identified, G61, describedbelow.

The human glioma cell line, G61 (Hamel et al., J. Neurosci. Res., 34:147-157 [1993]), was cultured in F12:DMEM (50:50) (high glucose)containing 10% fetal bovine serum, 2 mM L-glutamine, and antibiotics.For FACS analysis of Flt4/IgG binding to G61 cells, 1 million cells wereincubated with 70 nM receptor-IgG fusion protein in phosphate-bufferedsaline (PBS), 5% goat serum, 2% rabbit serum for 60 min. at 4° C. andthen stained with 10 μg/mL biotin-SP-conjugated goat anti-human Fcantibody and 10 μg/mL R-phycoerythrin-conjugated streptavidin (JacksonImmuno Research). G61 caused about a 10-fold shift in peak fluorescenceintensity that was specific for Flt4/IgG as compared to Rse/IgG, anunrelated tyrosine kinase receptor complex (FIG. 2). Attempts toexpression clone this putative membrane-bound VRP by the transfection ofpools of cDNA clones into COS cells followed by screening with labeledFlt4/IgG yielded no positives from 640 pools of 1000-5000 clones each.

EXAMPLE 3 Isolation of cDNA Clones Encoding Human VRP

A cDNA library was prepared from polyA+ RNA isolated as described inCathala et al., DNA: 2: 329-335 (1983) and Aviv and Leder, Proc. Natl.Acad. Sci. USA, 69: 1408-1412 (1972) from the human glioma cell line,G61. Hamel et al., supra. cDNA was prepared from this RNA with reagentsfrom GIBCO/BRL (SuperScript) and cloned in the plasmid pRK5B (Holmes etal., Science, 253: 1278-1280 [1991]) digested with XhoI and NotI. Clonesencoding VRP were isolated by screening the cDNA library with syntheticoligonucleotide probes based on an EST sequence (GenBank locusHSC1WF111), which showed a reasonable match to VEGF. The EST sequence ofHSC1WF111 is 299 bp and is 36% identical to VEGF over 50 residues,including an 11 of 13 residue match beginning at VEGF amino acid 56. Thesequence is as follows:

(SEQ ID NO: 6) 5′-CCGTCTACAGATGTGGGGGTTGCTGCAATAGTGAGGGGCTGCAGTGCATGAACACCAGCACGAGCTACCTCAGNAAGACGTTATTTGAAATTACAGTGCCTCTCTCTCAAGGCCCCAAACCAGTAACAATCAGTTTTGCCAATCACACTTCCTGCCGATGCATGTCTAAACTGGATGTTTACAGACAAGTTCATTCCATTATTAGACGTTCCCTGCCAGCAACACTACCACAGTGTCAGGCAGCGAACAAGACCTGCCCCACCAATTACATGTGGAATAATCACATCTGCAGATGCC TG.

The sequences of the oligonucleotide probes ovh1.4 and ovh1.5 employedare indicated below.

ovh1.4: (SEQ ID NO: 7)5′-CTGGTGTTCATGCACTGCAGCCCCTCACTATTGCAGCAACCCCCACA TCT ovh1.5: (SEQ IDNO: 8) 5′-GCATCTGCAGATGTGATTATTCCACATGTAATTGGTGGGGCAGGTCT TGT

These two probes were ³²P labeled and hybridized in 20% formamide at 42°C. with a final wash in 30 mM NaCl/3 mM trisodium citrate at 55° C.Janssen, Current Protocols in Molecular Biology, John Wiley & Sons(1995). Seven positives were identified and characterized from 650,000clones screened. The positives fell into three groups by restrictionmapping and DNA sequencing.

Clones VH1.4 (pRK.vh1.4.1) and VH1.6 included the full coding region(FIG. 3A) and were sequenced completely. They differ only in length andthe lack of two T's preceeding the 3′ poly A sequence in VH1.6. CloneVH1.2 is collinear with VH1.4. Clones VH1.3, VH1.5, and VH1.7 areidentical and have a 557 bp deletion when compared with VH1.4 (adeletion of bp 519-1075), and clone VH1.1 has a 152 bp deletion whencompared with VH1.4 (a deletion of bp 924-1075). The nucleotide anddeduced amino acid sequences of VH1.4 are shown in FIG. 1.

The sequence contained an open reading frame of 419 amino acidsbeginning with an ATG codon preceded by a purine residue at position −3as expected for a translation initiation site. Kozak, Nucl. Acids Res.,12: 857-872 (1984). About 250 bp 5′ of this ATG are two in-frame ATGcodons followed shortly (4 or 10 amino acids) by a stop codon. Both ofthese ATG's have a pyrimidine at position −3 and would not be expectedto function as a strong translation initiation site. Kozak, supra. Theencoded amino acid sequence imediately following the start of the 419amino acid reading frame is hydrophobic, indicative of an amino-terminalsecretion signal sequence. Perlman and Halvorson, J. Mol. Biol., 167:391-409 (1983). See FIG. 3A. The most likely cleavage site for thissequence would be after amino acid 20, although cleavage followingresidues 15 or 16 cannot be excluded. von Heijne, Nucl. Acids Res., 14:4683-4690 (1986). The open reading frame is preceded by a GC-rich 5′untranslated region of about 380 bp and followed by a 3′ untranslatedregion of about 400 bp.

The predicted mature amino acid sequence of human VRP contains 399 aminoacid residues (translated M_(r)=44.8 kDa), of which 37 (9.3%) arecysteine residues; there are three potential N-linked glycosylationsites (FIG. 3A). An alignment of the amino acid sequence of VRP with thesix forms of VEGF and PlGF shows that it is most similar to VEGF₁₂₁ (32%identical) and PlGF₁₃₁ (27% identical) (FIG. 3B); the locations of 8 ofthe 9 cysteine residues are conserved. While VRP does not contain theregions of basic amino acids found in some forms of VEGF and PlGF, it isconsiderably larger than VEGF and contains a cysteine-rich C-terminalhalf of the molecule that is not found in VEGF. This cysteine-richdomain has four copies of the pattern Cys followed by ten non-Cysresidues followed by Cys-X followed by Cys-X and then by Cys (FIG. 3B),a repeat found more than 50 times in a diptran Balbiani ring 3 protein.Paulsson et al., J. Mol. Biol., 211: 331-349 (1990). Without beinglimited to any one theory, VRP may interact with other membrane-boundproteins on these cells via the cysteine residues; such anintermolecular interaction has been proposed for the Balbiani protein.Paulsson et al., supra.

Two of the cDNA clones (VH1.1 and VH1.3) contained a 152 or 557 bpdeletion when compared with VH1.4 (FIG. 3A). Both these deletions end atthe same nucleotide and are presumed to be the result of alternativesplicing. Both deletions would be expected to encode the sameframe-shifted protein 3′ of the deletion which terminates at a stopcodon within 15 amino acids. The protein encoded by VH1.3 would includenone of the core cysteine region similar with VEGF. VH1.1 contains muchof the region that is similar to VEGF; its deletion, however, is notanalogous to the various known forms of VEGF or PlGF. Ferrara et al.,supra; Maglione et al., supra; Hauser and Weich, supra.

FIG. 4 discloses an alignment of VH1.4 (top) with 11 EST cDNA sequencesfrom GenBank. It is noted that the 3′ EST's are at the polyA end andthat the EST's cover only a little more than half of the full-lengthsequence of VH1.4.

EXAMPLE 4 Receptor IgG Precipitation of ³⁵S-Labeled VRP

To determine whether VRP is a ligand for Flt4, expression plasmidscontaining the VH1.4 cDNA clone, as well as control plasmids (theexpression vector alone or with VEGF or PlGF DNA), were transfected intoCOS7 cells and the proteins labeled with ³⁵S amino acids. Conditionedmedia from these cells was precipatated with Flt4/IgG and Flk1/IgG.Specifically, the VRP expression plasmid, pRK.vh1.4.2, was constructedby deleting about 360 bp of 5′ untranslated sequence (5′ of the AgeIsite (FIG. 3A) from VH1.4). This DNA and control plasmids encodingVEGF₁₆₅ (Houck et al., Mol. Endocrinol., 5: 1806-1814 [1991]), PlGF₁₅₂(Park et al., supra), or the vector alone (pRK5; Suva et al, supra) weretransfected into COS7 cells with DEAE-dextran. Janssen et al., supra.Two days after transfection, the cells were pulse-labeled in 10-cmdishes for 5 hours with 5 mL of methionine- and cysteine-free DMEMsupplemented with 100 μCi/mL of ³⁵S amino acids (Pro-Mix™ brand;Amersham #SJQ0079) at 37° C., and then chased with DMEM for 7 hours. Thelabeled conditioned medium was concentrated 10-fold by spinconcentration (Centricon-10™ brand; Amicon #4203). Fifty μL of theconcentrated medium was incubated with 3 μg of receptor IgG and 80 μL ofa 50% slurry of protein A agarose (Calbiochem) overnight at 4° C. Theprecipitates were washed with PBS/0.1% Triton X-100, boiled in SDSsample buffer, and electrophoresed on 12% SDS polyacrylamide gels (Novex#EC60052). The gels were treated with autoradiography enhancer (duPont#NEF974) and exposed overnight at −70° C.

Two specific bands of 53 kDa and 33 kDa were precipitated from the VRPtransfection by the Flt4/IgG; these bands were absent in the vectortransfection. Little or no specific precipitation of these two bands wasfound with Flt1/IgG or Flk1/IgG. At times, some VRP precipitation wasdetected with Flk1/IgG, suggesting that VRP may have a low-affinityinteraction with Flk1. Transfection with a VEGF-expressing plasmidshowed the expected precipitation of a strong band of about 22 kDa withFlt1/IgG and Flk1/IgG (DeVries et al., supra; Quinn et al., supra;Millauer et al., supra; Terman et al., Biochem. Biophys. Res. Commun.,supra), but no precipitation with Flt4/IgG. Similar experiments withlabeled PlGF showed no precipitation by Flt4/IgG, but did give theexpected precipitation by Flt1/IgG, but not by Flk1/IgG. Park et al.,supra. These data indicate that the VRP binds to the extracellulardomain of the Flt4 receptor, but does not interact (or does so much moreweakly) with the VEGF receptors Flt1 or Flk1. They also confirm the lackof an interaction of VEGF with Flt4 (Pajusola et al., Oncogene, 9,supra) and indicate that PlGF is also not a ligand for this receptor.

EXAMPLE 5 Tyrosine Phosphorylation of Flt4 Receptor

To assay Flt4 tyrosine phosphorylation (also described inPCT/US93/00586, supra), Flt4 was expressed in 293 cells and Flt4phosphorylation monitored by phosphotyrosine immunoblot. Specifically,DNA encoding the long form of human Flt4 was cloned into the mammalianexpression vector pRK5 (Suva et al., supra) to give the plasmidpRK.tk1-3.1. This plasmid was co-transfected with a plasmid containing amiroglycoside phosphotransferase (neo) transcription unit into 293 cellsby calcium phosphate precipitation (Janssen et al., supra), and stablytransfected lines were selected by growth on G418 (Gibco).

One clonal cell line expressing Flt4 (clone 31), as determined by FACSanalysis with Flt4/IgG antiserum, and untransfected 293 cells were usedin the Flt4 tyrosine phosphorylation assays. One million cells in 100 μLof PBS/0.1% bovine serum albumin (BSA) were mixed with 100 μL of sampleand incubated at 37° C. for 15 minutes. The cells were then collected bycentrifugation and lysed in 250 μL of 0.15 M NaCl, 10% glycerol, 1%Triton X-100, 50 mM HEPES pH 7.3, 4 μg/mL PMSF, 0.02 u/mL aprotinin(Sigma A6279), and 20 mM sodium orthovanadate. Flt4 wasimmunoprecipitated by the addition of 8 μL of rabbit Flt4/IgG antiserumand 30 μL of protein A agarose. Washed precipitates were boiled in SDSsample buffer, electrophoresed on polyacrylamide gels (Novex),transferred to nitrocellulose (Janssen et al., supra), and probed withan anti-phosphotyrosine monoclonal antibody (Upstate Biotechnology) andan alkaline phosphatase detection system (Promega).

Samples containing VRP or VEGF were prepared by the electroporation ofexpression plasmids encoding VH1.4 (pRK.vh1.4.2) or VEGF (Houck et al.,supra) into 293 cells and 20-fold concentration (Centricon-10, Amicon)of the 3-day serum-free conditioned medium. In the receptor IgGcompetition experiments, the concentrated conditioned media werepre-incubated 1 hour at 4° C. with receptor IgG.

Without stimulation, 293 cells expressing or not expressing Flt4 showedlittle or no Flt4 tyrosine phosphorylation. Stimulation of theFlt4-expressing cells by Flt4/IgG antiserum showed the tyrosinephosphorylation of two bands of 180 and 120 kDa. No increase above basalphosphorylation was observed with preimmune serum, and no bands werefound with Flt4/IgG antiserum stimulation of non-expressing cells. TwoFlt4 bands of about this size have been reported as being expressed byDAMI and HEL cells. Pajusola et al., Oncogene, 8, supra. In addition,SDS gel analysis of purified Flt4/IgG shows that it is composed ofpeptides of 150, 80, and 70 kDa. N-terminal amino acid sequence of theFlt4/IG peptides shows that the 150 and 70 kDa bands have the amino acidsequence YSMTPPTL (SEQ ID NO: 9) (matching the Flt4 sequence starting atresidue 25) and that the 80 kDa band has the sequence SLRRRQQQD (SEQ IDNO: 10) (matching the Flt4 sequence beginning at residue 473). Thus,both the Flt4/IgG and full-length Flt4 appear to be partially cleaved inthe extracellular domain, and the tyrosine phosphorylated bands of 180and 120 kDa observed in the Flt4 phosphorylation assays would correspondto the 150 and 80 kDa peptides of Flt4/IgG. Addition of a polyclonalantiserum to the Flt4 expressing cells showed the tyrosinephosphorylation of two Flt4 bands of 180 and 120 kDa; no bands wereobserved in non-expressing cells. These data show that polyclonalantibodies generated to the extracellular domain of the Flt4 receptorare capable of activating Flt4 tyrosine phosphorylation.

To determine whether VRP could activate the tyrosine phosphorylation ofFlt4, conditioned media from mammalian cells transfected with the VRPexpression plasmid was assayed. This conditioned medium stimulated thetyrosine phosphorylation of the same 180 and 120 kDa bands found withthe agonist polyclonal antibodies, demonstrating that VRP is able tostimulate the phosphorylation of, as well as bind to, Flt4. Conditionedmedium from VEGF-expressing cells failed to activate Flt4 tyrosinephosphorylation.

To confirm the specificity of VRP binding to the receptors of the VEGFfamily, Flt4/IgG, Flt1/IgG, Flk1/IgG, and Htk/IgG were tested for theirability to compete for VRP-stimulated Flt4 phosphorylation. As expectedif VRP is a ligand for Flt4, Flt4/IgG prevented the VRP-stimulatedphosphorylation, while Flt1/IgG, Flk1/IgG, and Htk/IgG, a fusion proteinfrom an unrelated tyrosine kinase receptor, had little or no effect.These data show that VRP is able to induce the tyrosine phosphorylationof Flt4.

EXAMPLE 6 Purification of VRP and Binding to Labeled Flt4/IgG

The reading frame encoding the N-terminal secretion signal sequence andabout 30 amino acids of the herpes glycoprotein D (Lasky and Dowbenko,DNA, 3: 23-29 [1984]; Pennica et al., Proc. Natl. Acad. Sci. USA, 92:1142-1146 [1995]) were fused with a short linker sequence to theputative mature sequence of VRP. Following secretion from mammaliancells, this construct is expected to give the N-terminal glycoprotein Dsequence: KYALADASLKMADPNRFRGKDLPVLDQLLEGGAAHYALLP (SEQ ID NO: 11)followed by the mature VRP sequence GPREAPAAAAAFE (SEQ ID NO: 12). DNAencoding this fusion protein was cloned into the vector pRK5 to give theplasmid pRK.vh1.4.5. This plasmid was transfected into 293 cells byelectroporation (Janssen et al., supra), and VRP purified from the 3-4day serum-free conditioned medium by monoclonal antibody (5B6) affinitychromatography and quantitated by calorimetric assay (Bio-Rad). Thisantibody is specific for the glycoprotein D sequence fused to theN-terminus of VRP.

Flt4/IgG was iodinated to a specific activity of 1000-1500 Ci/mmol withIodobeads™ brand iodinated beads (Pierce). Binding was performed with˜20,000 cpm ¹²⁵I-Flt4/IgG and 12 ng VH1.4 gD fusion protein in PBS, 0.5%BSA, 0.02% Tween-20™ surfactant, 1 μg/mL heparin (binding buffer)containing 20 μL of a 50% slurry of glass beads conjugated to ˜30 μganti-gD monoclonal antibody (5B6) in a final volume of 100 μL for 4-6hours at 22° C. Beads were collected by filtration (MilliporeMultiscreen-HV), washed five times with 200 μL binding buffer, andcounted. For binding at increasing concentrations of Flt4/IgG (FIG. 5B)the binding buffer was DMEM (low glucose):F12 (50:50), 20 mM sodiumHEPES, pH 7.2, 10% fetal bovine serum, 0.2% gelatin, and 1 μg/mLheparin.

The purified VRP specifically bound to ¹²⁵I-Flt4/IgG, and the bindingwas not competed by unlabeled Flt1/IgG or Flk1/IgG (FIG. 5A). Bindingcompetition with increasing concentrations of unlabeled Flt4/IgG (FIG.5B) gave an EC₅₀ for this interaction of ˜0.7 nM, suggesting that thebinding of VRP to Flt4 is of high affinity as would be expected if VRPis a biologically relevant ligand for Flt4.

RNA Blots

Blots containing poly(A)+ human RNA were from Clontech. For the G61glioma cell line, 5 μg of poly(A)+ and poly(A)− RNA were electrophoresedon a 1% agarose/2.2 M formaldehyde gel and transferred to nitrocellulose(Janssen et al., supra). Blots were hybridized with ³²P-labeled probesovh1.4 and ovh1.5 and washed in 30 mM NaCl/3 mM trisodium citrate at 55°C.

The G61 glioma cell line used in the cloning of VRP expresses a majorVRP RNA band of about 2.4 kb. A minor band of about 2.2 kb may also bepresent. A 2.4 kb band was expressed in adult human tissues from heart,placenta, ovary, and small intestine; a weaker band was found in lung,skeletal muscle, spleen, prostrate, testis, and colon. Expression of a2.4 kb mRNA was also found in fetal lung and kidney.

EXAMPLE 7 Mitogenic Activity of VRP

To test whether VRP has mitogenic activity like that found for VEGF, thegrowth of human lung endothelial cells was determined at increasingconcentrations of VRP or VEGF (FIG. 6). Specifically, human lungmicrovascular endothelial cells (HMVEC-L, Clonetics, San Diego, Calif.)were maintained in the recommended growth medium (EGM-MV with 5% fetalcalf serum). For the assay of mitogenesis, low passage (<6) cells wereseeded at 6500 cells/well in 48-well plates (Costar) and maintainedovernightin the recommended growth medium. The medium was removed, andthe cells were maintained in the growth medium (2% fetal calf serum)without bovine brain extract and supplemented with VEGF or VRP. Afterfour days, the cells were removed with trypsin and counted with aCoulter counter (Hialeah, Fla.).

VRP promoted the growth of these endothelial cells (see FIG. 6), andthus shares this mitogenic activity with VEGF. This is in contrast toPlGF, which has been reported to lack such mitogenic activity (at ≦35nM). Park et al., supra. While an effective mitogenic agent, VRP wasabout 100 fold less potent than VEGF in this assay.

In conclusion, a novel secreted protein, VRP, has now been identifiedthat is a Flt4 ligand and that stimulates the tyrosine phosphorylationof the receptor tyrosine kinase Flt4. VRP is a third member of the VEGFprotein family and has about 30% amino acid identity with VEGF and PlGF.In addition to the VEGF-like domain, VRP contains a ˜180 amino acidC-terminal, cysteine-rich domain not found in other members of the VEGFfamily. VRP fails to interact appreciably with the VEGF receptors Flt1and Flk1.

Deposit of Material

The following plasmid has been deposited with the American Type CultureCollection, 12301 Parklawn Drive, Rockville, Md., USA (ATCC):

Plasmid ATCC Dep. No. Deposit Date pRK.vh1.4.1 97249 Sep. 6, 1995

This deposit was made under the provisions of the Budapest Treaty on theInternational Recognition of the Deposit of Microorganisms for thePurpose of Patent Procedure and the Regulations thereunder (BudapestTreaty). This assures maintenance of a viable culture of the deposit for30 years from the date of deposit. The deposit will be made available byATCC under the terms of the Budapest Treaty, and subject to an agreementbetween Genentech, Inc. and ATCC, which assures permanent andunrestricted availability of the progeny of the culture of the depositto the public upon issuance of the pertinent U.S. patent or upon layingopen to the public of any U.S. or foreign patent application, whichevercomes first, and assures availability of the progeny to one determinedby the U.S. Commissioner of Patents and Trademarks to be entitledthereto according to 35 USC § 122 and the Commissioner's rules pursuantthereto (including 37 CFR § 1.14 with particular reference to 886 OG638).

The assignee of the present application has agreed that if a culture ofthe plasmid on deposit should die or be lost or destroyed whencultivated under suitable conditions, the plasmid will be promptlyreplaced on notification with another of the same plasmid. Availabilityof the deposited plasmid is not to be construed as a license to practicethe invention in contravention of the rights granted under the authorityof any government in accordance with its patent laws.

The foregoing written specification is considered to be sufficient toenable one skilled in the art to practice the invention. The presentinvention is not to be limited in scope by the construct deposited,since the deposited embodiment is intended as a single illustration ofcertain aspects of the invention and any constructs that arefunctionally equivalent are within the scope of this invention. Thedeposit of material herein does not constitute an admission that thewritten description herein contained is inadequate to enable thepractice of any aspect of the invention, including the best modethereof, nor is it to be construed as limiting the scope of the claimsto the specific illustrations that it represents. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description and fall within the scope of the appended claims.

1. An isolated nucleic acid molecule encoding a VEGF-related protein(VRP), wherein said VRP comprises an amino acid sequence selected fromthe group consisting of residues −20 to 399 of FIG. 1 (residues 1 to 419of SEQ ID NO:3) and residues 1 to 399 of FIG. 1 (residues 21 to 419 ofSEQ ID NO:3).
 2. An expression vector comprising the nucleic acidmolecule of claim
 1. 3. A process for preparing a VRP polypeptide,comprising culturing a host cell transformed with the vector of claim 2under conditions promoting expression of VRP and recovering the VRPpolypeptide.
 4. An isolated nucleic acid molecule comprising anucleotide sequence selected from the group consisting of nucleotides372 to 1628 of SEQ ID NO:1 and nucleotides 432 to 1628 of SEQ ID NO:1.5. An expression vector comprising the nucleic acid molecule of claim 4.6. A process for preparing a VRP polypeptide, comprising culturing ahost cell transformed with the vector of claim 5 under conditionspromoting expression of VRP and recovering the VRP polypeptide.
 7. Anisolated nucleic acid molecule encoding a VRP polypeptide, wherein saidnucleic acid molecule comprises the VRP cDNA insert of vector depositedin strain ATCC
 97249. 8. An expression vector comprising the nucleicacid molecule of claim
 7. 9. A process for preparing, a VRP polypeptide,comprising culturing a host cell transformed with a vector of claim 8under conditions promoting expression of VRP polypeptide.